4. Types

In PowerShell, each value has a type, and types fall into one of two main categories: value types and reference types. Consider the type int, which is typical of value types. A value of type int is completely self-contained; all the bits needed to represent that value are stored in that value, and every bit pattern in that value represents a valid value for its type. Now, consider the array type int[], which is typical of reference types. A so-called value of an array type can hold either a reference to an object that actually contains the array elements, or the null reference whose value is $null. The important distinction between the two type categories is best demonstrated by the differences in their semantics during assignment. For example,

$i = 100 # $i designates an int value 100
$j = $i # $j designates an int value 100, which is a copy

$a = 10,20,30 # $a designates an object[], Length 3, value 10,20,30
$b = $a # $b designates exactly the same array as does $a, not a copy
$a[1] = 50 # element 1 (which has a value type) is changed from 20 to 50
$b[1] # $b refers to the same array as $a, so $b[1] is 50

As we can see, the assignment of a reference type value involves a shallow copy; that is, a copy of the reference to the object rather than its actual value. In contrast, a deep copy requires making a copy of the object as well.

A numeric type is one that allows representation of integer or fractional values, and that supports arithmetic operations on those values. The set of numerical types includes the integer (§4.2.3) and real number (§4.2.4) types, but does not include bool (§4.2.1) or char (§4.2.2). An implementation may provide other numeric types (such as signed byte, unsigned integer, and integers of other sizes).

A collection is a group of one or more related items, which need not have the same type. Examples of collection types are arrays, stacks, queues, lists, and hash tables. A program can enumerate (or iterate) over the elements in a collection, getting access to each element one at a time. Common ways to do this are with the foreach statement (§8.4.4) and the ForEach-Object cmdlet. The type of an object that represents an enumerator is described in §4.5.16.

In this chapter, there are tables that list the accessible members for a given type. For methods, the Type is written with the following form: returnType/argumentTypeList. If the argument type list is too long to fit in that column, it is shown in the Purpose column instead.

Other integer types are SByte, Int16, UInt16, UInt32, and UInt64, all in the namespace System.

Many collection classes are defined as part of the System.Collections or System.Collections.Generic namespaces. Most collection classes implement the interfaces ICollection, IComparer, IEnumerable, IList, IDictionary, and IDictionaryEnumerator and their generic equivalents.

You can also use shorthand names for some types. For more information, see about_Type_Accelerators.

4.1 Special types

4.1.1 The void type

This type cannot be instantiated. It provides a means to discard a value explicitly using the cast operator (§7.2.9).

4.1.2 The null type

The null type has one instance, the automatic variable $null (§2.3.2.2), also known as the null value. This value provides a means for expressing "nothingness" in reference contexts. The characteristics of this type are unspecified.

4.1.3 The object type

Every type in PowerShell except the null type (§4.1.2) is derived directly or indirectly from the type object, so object is the ultimate base type of all non-null types. A variable constrained (§5.3) to type object is really not constrained at all, as it can contain a value of any type.

4.2 Value types

4.2.1 Boolean

The Boolean type is bool. There are only two values of this type, False and True, represented by the automatic variables $false and $true, respectively (§2.3.2.2).

In PowerShell, bool maps to System.Boolean.

4.2.2 Character

A character value has type char, which is capable of storing any UTF-16-encoded 16-bit Unicode code point.

The type char has the following accessible members:

Member	Member Kind	Type	Purpose
MaxValue	Static property (read-only)	char	The largest possible value of type char
MinValue	Static property (read-only)	char	The smallest possible value of type char
IsControl	Static method	bool/char	Tests if the character is a control character
IsDigit	Static method	bool/char	Tests if the character is a decimal digit
IsLetter	Static method	bool/char	Tests if the character is an alphabetic letter
IsLetterOrDigit	Static method	bool/char	Tests if the character is a decimal digit or alphabetic letter
IsLower	Static method	bool/char	Tests if the character is a lowercase alphabetic letter
IsPunctuation	Static method	bool/char	Tests if the character is a punctuation mark
IsUpper	Static method	bool/char	Tests if the character is an uppercase alphabetic letter
IsWhiteSpace	Static method	bool/char	Tests if the character is a white space character.
ToLower	Static method	char/string	Converts the character to lowercase
ToUpper	Static method	char/string	Converts the character to uppercase

Windows PowerShell: char maps to System.Char.

4.2.3 Integer

There are two signed integer types, both of use two's-complement representation for negative values:

• Type int, which uses 32 bits giving it a range of -2147483648 to +2147483647, inclusive.
• Type long, which uses 64 bits giving it a range of -9223372036854775808 to +9223372036854775807, inclusive.

Type int has the following accessible members:

Member	Member Kind	Type	Purpose
MaxValue	Static property (read-only)	int	The largest possible value of type int
MinValue	Static property (read-only)	int	The smallest possible value of type int

Type long has the following accessible members:

Member	Member Kind	Type	Purpose
MaxValue	Static property (read-only)	long	The largest possible value of type long
MinValue	Static property (read-only)	long	The smallest possible value of type long

There is one unsigned integer type:

• Type byte, which uses 8 bits giving it a range of 0 to 255, inclusive.

Type byte has the following accessible members:

Member	Member Kind	Type	Purpose
MaxValue	Static property (read-only)	byte	The largest possible value of type byte
MinValue	Static property (read-only)	byte	The smallest possible value of type byte

In PowerShell, byte, int, and long map to System.Byte, System.Int32, and System.Int64, respectively.

4.2.4 Real number

4.2.4.1 float and double

There are two real (or floating-point) types:

• Type float uses the 32-bit IEEE single-precision representation.
• Type double uses the 64-bit IEEE double-precision representation.

A third type name, single, is a synonym for type float; float is used throughout this specification.

Although the size and representation of the types float and double are defined by this specification, an implementation may use extended precision for intermediate results.

Type float has the following accessible members:

Member	Member Kind	Type	Purpose
MaxValue	Static property (read-only)	float	The largest possible value of type float
MinValue	Static property (read-only)	float	The smallest possible value of type float
NaN	Static property (read-only)	float	The constant value Not-a-Number
NegativeInfinity	Static property (read-only)	float	The constant value negative infinity
PositiveInfinity	Static property (read-only)	float	The constant value positive infinity

Type double has the following accessible members:

Member	Member Kind	Type	Purpose
MaxValue	Static property (read-only)	double	The largest possible value of type double
MinValue	Static property (read-only)	double	The smallest possible value of type double
NaN	Static property (read-only)	double	The constant value Not-a-Number
NegativeInfinity	Static property (read-only)	double	The constant value negative infinity
PositiveInfinity	Static property (read-only)	double	The constant value positive infinity

In PowerShell, float and double map to System.Single and System.Double, respectively.

4.2.4.2 decimal

Type decimal uses a 128-bit representation. At a minimum it must support a scale s such that 0 <= s <= at least 28, and a value range -79228162514264337593543950335 to 79228162514264337593543950335. The actual representation of decimal is implementation defined.

Type decimal has the following accessible members:

Member	Member Kind	Type	Purpose
MaxValue	Static property (read-only)	decimal	The largest possible value of type decimal
MinValue	Static property (read-only)	decimal	The smallest possible value of type decimal

Note

Decimal real numbers have a characteristic called scale, which represents the number of digits to the right of the decimal point. For example, the value 2.340 has a scale of 3 where trailing zeros are significant. When two decimal real numbers are added or subtracted, the scale of the result is the larger of the two scales. For example, 1.0 + 2.000 is 3.000, while 5.0 - 2.00 is 3.00. When two decimal real numbers are multiplied, the scale of the result is the sum of the two scales. For example, 1.0 * 2.000 is 2.0000. When two decimal real numbers are divided, the scale of the result is the scale of the first less the scale of the second. For example, 4.00000/2.000 is 2.00. However, a scale cannot be less than that needed to preserve the correct result. For example, 3.000/2.000, 3.00/2.000, 3.0/2.000, and 3/2 are all 1.5.

In PowerShell, decimal maps to System.Decimal. The representation of decimal is as follows:

• When considered as an array of four int values it contains the following elements:
  • Index 0 (bits 0‑31) contains the low-order 32 bits of the decimal's coefficient.
  • Index 1 (bits 32‑63) contains the middle 32 bits of the decimal's coefficient.
  • Index 2 (bits 64‑95) contains the high-order 32 bits of the decimal's coefficient.
  • Index 3 (bits 96‑127) contains the sign bit and scale, as follows:
    • bits 0--15 are zero
    • bits 16‑23 contains the scale as a value 0--28
    • bits 24‑30 are zero
    • bit 31 is the sign (0 for positive, 1 for negative)

4.2.5 The switch type

This type is used to constrain the type of a parameter in a command (§8.10.5). If an argument having the corresponding parameter name is present the parameter tests $true; otherwise, it tests $false.

In PowerShell, switch maps to System.Management.Automation.SwitchParameter.

4.2.6 Enumeration types

An enumeration type is one that defines a set of named constants representing all the possible values that can be assigned to an object of that enumeration type. In some cases, the set of values are such that only one value can be represented at a time. In other cases, the set of values are distinct powers of two, and by using the -bor operator (§7.8.5), multiple values can be encoded in the same object.

The PowerShell environment provides a number of enumeration types, as described in the following sections.

4.2.6.1 Action-Preference type

This implementation-defined type has the following mutually exclusive-valued accessible members:

Member	Member Kind	Purpose
Continue	Enumeration constant	The PowerShell runtime will continue processing and notify the user that an action has occurred.
Inquire	Enumeration constant	The PowerShell runtime will stop processing and ask the user how it should proceed.
SilentlyContinue	Enumeration constant	The PowerShell runtime will continue processing without notifying the user that an action has occurred.
Stop	Enumeration constant	The PowerShell runtime will stop processing when an action occurs.

In PowerShell, this type is System.Management.Automation.ActionPreference.

4.2.6.2 Confirm-Impact type

This implementation-defined type has the following mutually exclusive-valued accessible members:

Member	Member Kind	Purpose
High	Enumeration constant	The action performed has a high risk of losing data, such as reformatting a hard disk.
Low	Enumeration constant	The action performed has a low risk of losing data.
Medium	Enumeration constant	The action performed has a medium risk of losing data.
None	Enumeration constant	Do not confirm any actions (suppress all requests for confirmation).

In PowerShell, this type is System.Management.Automation.ConfirmImpact.

4.2.6.3 File-Attributes type

This implementation-defined type has the following accessible members, which can be combined:

Member	Member Kind	Purpose
Archive	Enumeration constant	The file's archive status. Applications use this attribute to mark files for backup or removal.
Compressed	Enumeration constant	The file is compressed.
Device		Reserved for future use.
Directory	Enumeration constant	The file is a directory.
Encrypted	Enumeration constant	The file or directory is encrypted. For a file, this means that all data in the file is encrypted. For a directory, this means that encryption is the default for newly created files and directories.
Hidden	Enumeration constant	The file is hidden, and thus is not included in an ordinary directory listing.
Normal	Enumeration constant	The file is normal and has no other attributes set. This attribute is valid only if used alone.
NotContentIndexed	Enumeration constant	The file will not be indexed by the operating system's content indexing service.
Offline	Enumeration constant	The file is offline. The data of the file is not immediately available.
ReadOnly	Enumeration constant	The file is read-only.
ReparsePoint	Enumeration constant	The file contains a reparse point, which is a block of user-defined data associated with a file or a directory.
SparseFile	Enumeration constant	The file is a sparse file. Sparse files are typically large files whose data are mostly zeros.
System	Enumeration constant	The file is a system file. The file is part of the operating system or is used exclusively by the operating system.
Temporary	Enumeration constant	The file is temporary. File systems attempt to keep all of the data in memory for quicker access rather than flushing the data back to mass storage. A temporary file should be deleted by the application as soon as it is no longer needed.

In PowerShell, this type is System.IO.FileAttributes with attribute FlagsAttribute.

4.2.6.4 Regular-Expression-Option type

This implementation-defined type has the following accessible members, which can be combined:

Member	Member Kind	Purpose
IgnoreCase	Enumeration constant	Specifies that the matching is case-insensitive.
None	Enumeration constant	Specifies that no options are set.

An implementation may provide other values.

In PowerShell, this type is System.Text.RegularExpressions.RegexOptions with attribute FlagsAttribute. The following extra values are defined: Compiled, CultureInvariant, ECMAScript, ExplicitCapture, IgnorePatternWhitespace, Multiline, RightToLeft, Singleline.

4.3 Reference types

4.3.1 Strings

A string value has type string and is an immutable sequence of zero or more characters of type char each containing a UTF-16-encoded 16-bit Unicode code point.

Type string has the following accessible members:

Member	Member Kind	Type	Purpose
Length	Instance Property	int (read-only)	Gets the number of characters in the string
ToLower	Instance Method	string	Creates a new string that contains the lowercase equivalent
ToUpper	Instance Method	string	Creates a new string that contains the uppercase equivalent

In PowerShell, string maps to System.String.

4.3.2 Arrays

All array types are derived from the type Array. This type has the following accessible members:

Member	Member Kind	Type	Purpose
Length	Instance Property (read-only)	int	Number of elements in the array
Rank	Instance Property (read-only)	int	Number of dimensions in the array
Copy	Static Method	void/see Purpose column	Copies a range of elements from one array to another. There are four versions, where source is the source array, destination is the destination array, count is the number of elements to copy, and sourceIndex and destinationIndex are the starting locations in their respective arrays: Copy(source, destination, int count) Copy(source, destination, long count) Copy(source, sourceIndex, destination, destinationIndex, int count) Copy(source, sourceIndex, destination, destinationIndex, long count)
GetLength	Instance Method (read-only)	int/none	Number of elements in a given dimension GetLength(int dimension)

For more details on arrays, see §9.

In PowerShell, Array maps to System.Array.

4.3.3 Hashtables

Type Hashtable has the following accessible members:

Member	Member Kind	Type	Purpose
Count	Instance Property	int	Gets the number of key/value pairs in the Hashtable
Keys	Instance Property	Implementation-defined	Gets a collection of all the keys
Values	Instance Property	Implementation-defined	Gets a collection of all the values
Remove	Instance Method	void/none	Removes the designated key/value

For more details on Hashtables, see §10.

In PowerShell, Hashtable maps to System.Collections.Hashtable. Hashtable elements are stored in an object of type DictionaryEntry, and the collections returned by Keys and Values have type ICollection.

4.3.4 The xml type

Type xml implements the W3C Document Object Model (DOM) Level 1 Core and the Core DOM Level 2. The DOM is an in-memory (cache) tree representation of an XML document and enables the navigation and editing of this document. This type supports the subscript operator [] (§7.1.4.4).

In PowerShell, xml maps to System.Xml.XmlDocument.

4.3.5 The regex type

Type regex provides machinery for supporting regular expression processing. It is used to constrain the type of a parameter (§5.3) whose corresponding argument might contain a regular expression.

In PowerShell, regex maps to System.Text.RegularExpressions.Regex.

4.3.6 The ref type

Ordinarily, arguments are passed to commands by value. In the case of an argument having some value type a copy of the value is passed. In the case of an argument having some reference type a copy of the reference is passed.

Type ref provides machinery to allow arguments to be passed to commands by reference, so the commands can modify the argument's value. Type ref has the following accessible members:

Member	Member Kind	Type	Purpose
Value	Instance property (read-write)	The type of the value being referenced.	Gets/sets the value being referenced.

Consider the following function definition and call:

function Doubler {
    param ([ref]$x) # parameter received by reference
    $x.Value *= 2.0 # note that 2.0 has type double
}

$number = 8 # designates a value of type int, value 8
Doubler([ref]$number) # argument received by reference
$number # designates a value of type double, value 8.0

Consider the case in which $number is type-constrained:

[int]$number = 8 # designates a value of type int, value 8
Doubler([ref]$number) # argument received by reference
$number # designates a value of type int, value 8

As shown, both the argument and its corresponding parameter must be declared ref.

In PowerShell, ref maps to System.Management.Automation.PSReference.

4.3.7 The scriptblock type

Type scriptblock represents a precompiled block of script text (§7.1.8) that can be used as a single unit. It has the following accessible members:

Member	Member Kind	Type	Purpose
Attributes	Instance property (read-only)	Collection of attributes	Gets the attributes of the script block.
File	Instance property (read-only)	string	Gets the name of the file in which the script block is defined.
Module	Instance property (read-only)	implementation defined ([§4.5.12][§4.5.12])	Gets information about the module in which the script block is defined.
GetNewClosure	Instance method	scriptblock /none	Retrieves a script block that is bound to a module. Any local variables that are in the context of the caller will be copied into the module.
Invoke	Instance method	Collection of object/object[]	Invokes the script block with the specified arguments and returns the results.
InvokeReturnAsIs	Instance method	object/object[]	Invokes the script block with the specified arguments and returns any objects generated.
Create	Static method	scriptblock /string	Creates a new scriptblock object that contains the specified script.

In PowerShell, scriptblock maps to System.Management.Automation.ScriptBlock. Invoke returns a collection of PSObject.

4.3.8 The math type

Type math provides access to some constants and methods useful in mathematical computations. It has the following accessible members:

Member	Member Kind	Type	Purpose
E	Static property (read-only)	double	Natural logarithmic base
PI	Static property (read-only)	double	Ratio of the circumference of a circle to its diameter
Abs	Static method	numeric/numeric	Absolute value (the return type is the same as the type of the argument passed in)
Acos	Static method	double / double	Angle whose cosine is the specified number
Asin	Static method	double / double	Angle whose sine is the specified number
Atan	Static method	double / double	Angle whose tangent is the specified number
Atan2	Static method	double / double y, double x	Angle whose tangent is the quotient of two specified numbers x and y
Ceiling	Static method	decimal / decimal double / double	smallest integer greater than or equal to the specified number
Cos	Static method	double / double	Cosine of the specified angle
Cosh	Static method	double / double	Hyperbolic cosine of the specified angle
Exp	Static method	double / double	e raised to the specified power
Floor	Static method	decimal / decimal double / double	Largest integer less than or equal to the specified number
Log	Static method	double / double number double / double number, double base	Logarithm of number using base e or base base
Log10	Static method	double / double	Base-10 logarithm of a specified number
Max	Static method	numeric/numeric	Larger of two specified numbers (the return type is the same as the type of the arguments passed in)
Min	Static method	numeric/numeric, numeric	Smaller of two specified numbers (the return type is the same as the type of the arguments passed in)
Pow	Static method	double / double x, double y	A specified number x raised to the specified power y
Sin	Static method	double / double	Sine of the specified angle
Sinh	Static method	double / double	Hyperbolic sine of the specified angle
Sqrt	Static method	double / double	Square root of a specified number
Tan	Static method	double / double	Tangent of the specified angle
Tanh	Static method	double / double	Hyperbolic tangent of the specified angle

In PowerShell, Math maps to System.Math.

4.3.9 The ordered type

Type ordered is a pseudo type used only for conversions.

4.3.10 The pscustomobject type

Type pscustomobject is a pseudo type used only for conversions.

4.4 Generic types

A number of programming languages and environments provide types that can be specialized. Many of these types are referred to as container types, as instances of them are able to contain objects of some other type. Consider a type called Stack that can represent a stack of values, which can be pushed on and popped off. Typically, the user of a stack wants to store only one kind of object on that stack. However, if the language or environment does not support type specialization, multiple distinct variants of the type Stack must be implemented even though they all perform the same task, just with different type elements.

Type specialization allows a generic type to be implemented such that it can be constrained to handling some subset of types when it is used. For example,

• A generic stack type that is specialized to hold strings might be written as Stack[string].
• A generic dictionary type that is specialized to hold int keys with associated string values might be written as Dictionary[int,string].
• A stack of stack of strings might be written as Stack[Stack[string]].

Although PowerShell does not define any built-in generic types, it can use such types if they are provided by the host environment. See the syntax in §7.1.10.

The complete name for the type Stack[string] suggested above is System.Collections.Generic.Stack[string]. The complete name for the type Dictionary[int,string] suggested above is System.Collections.Generic.Dictionary[int,string].

4.5 Anonymous types

In some circumstances, an implementation of PowerShell creates objects of some type, and those objects have members accessible to script. However, the actual name of those types need not be specified, so long as the accessible members are specified sufficiently for them to be used. That is, scripts can save objects of those types and access their members without actually knowing those types' names. The following subsections specify these types.

4.5.1 Provider description type

This type encapsulates the state of a provider. It has the following accessible members:

Member	Member Kind	Type	Purpose
Drives	Instance property (read-only)	Implementation defined (§4.5.2)	A collection of drive description objects
Name	Instance property (read-only)	string	The name of the provider

In PowerShell, this type is System.Management.Automation.ProviderInfo.

4.5.2 Drive description type

This type encapsulates the state of a drive. It has the following accessible members:

Member	Member Kind	Type	Purpose
CurrentLocation	Instance property (read-write)	string	The current working location (§3.1.4) of the drive
Description	Instance property (read-write)	string	The description of the drive
Name	Instance property (read-only)	string	The name of the drive
Root	Instance property (read-only)	string	The name of the drive

In PowerShell, this type is System.Management.Automation.PSDriveInfo.

4.5.3 Variable description type

This type encapsulates the state of a variable. It has the following accessible members:

Member	Member Kind	Type	Purpose
Attributes	Instance property (read-only)	Implementation defined	A collection of attributes
Description	Instance property (read-write)	string	The description assigned to the variable via the New-Variable or Set-Variable cmdlets.
Module	Instance property (read-only)	Implementation defined (§4.5.12)	The module from which this variable was exported
ModuleName	Instance property (read-only)	string	The module in which this variable was defined
Name	Instance property (read-only)	string	The name assigned to the variable when it was created in the PowerShell language or via the New-Variable and Set-Variable cmdlets.
Options	Instance property (read-write)	string	The options assigned to the variable via the New-Variable and Set-Variable cmdlets.
Value	Instance property (read-write)	object	The value assigned to the variable when it was assigned in the PowerShell language or via the New-Variable and Set-Variable cmdlets.

In PowerShell, this type is System.Management.Automation.PSVariable.

Windows PowerShell: The type of the attribute collection is System.Management.Automation.PSVariableAttributeCollection.

4.5.4 Alias description type

This type encapsulates the state of an alias. It has the following accessible members:

Member	Member Kind	Type	Purpose
CommandType	Instance property (read-only)	Implementation defined	Should compare equal with "Alias".
Definition	Instance property (read-only)	string	The command or alias to which the alias was assigned via the New-Alias or Set-Alias cmdlets.
Description	Instance property (read-write)	string	The description assigned to the alias via the New-Alias or Set-Alias cmdlets.
Module	Instance property (read-only)	Implementation defined (§4.5.12)	The module from which this alias was exported
ModuleName	Instance property (read-only)	string	The module in which this alias was defined
Name	Instance property (read-only)	string	The name assigned to the alias when it was created via the New-Alias or Set-Alias cmdlets.
Options	Instance property (read-write)	string	The options assigned to the alias via the New-Alias New-Alias or Set-Alias cmdlets.
OutputType	Instance property (read-only)	Implementation defined collection	Specifies the types of the values output by the command to which the alias refers.
Parameters	Instance property (read-only)	Implementation defined collection	The parameters of the command.
ParameterSets	Instance property (read-only)	Implementation defined collection	Information about the parameter sets associated with the command.
ReferencedCommand	Instance property (read-only)	Implementation defined	Information about the command that is immediately referenced by this alias.
ResolvedCommand	Instance property (read-only)	Implementation defined	Information about the command to which the alias eventually resolves.

In PowerShell, this type is System.Management.Automation.AliasInfo.

4.5.5 Working location description type

This type encapsulates the state of a working location. It has the following accessible members:

Member	Member Kind	Type	Purpose
Drive	Instance property (read-only)	Implementation defined (§4.5.2)	A drive description object
Path	Instance property (read-only)	string	The working location
Provider	Instance property (read-only)	Implementation defined (§4.5.1)	The provider
ProviderPath	Instance property (read-only)	string	The current path of the provider

A stack of working locations is a collection of working location objects, as described above.

In PowerShell, a current working location is represented by an object of type System.Management.Automation.PathInfo. A stack of working locations is represented by an object of type System.Management.Automation.PathInfoStack, which is a collection of PathInfo objects.

4.5.6 Environment variable description type

This type encapsulates the state of an environment variable. It has the following accessible members:

Member	Member Kind	Type	Purpose
Name	Instance property (read-write)	string	The name of the environment variable
Value	Instance property (read-write)	string	The value of the environment variable

In PowerShell, this type is System.Collections.DictionaryEntry. The name of the variable is the dictionary key. The value of the environment variable is the dictionary value. Name is an AliasProperty that equates to Key.

4.5.7 Application description type

This type encapsulates the state of an application. It has the following accessible members:

Member	Member Kind	Type	Purpose
CommandType	Instance property (read-only)	Implementation defined	Should compare equal with "Application".
Definition	Instance property (read-only)	string	A description of the application.
Extension	Instance property (read-write)	string	The extension of the application file.
Module	Instance property (read-only)	Implementation defined (§4.5.12)	The module that defines this command.
ModuleName	Instance property (read-only)	string	The name of the module that defines the command.
Name	Instance property (read-only)	string	The name of the command.
OutputType	Instance property (read-only)	Implementation defined collection	Specifies the types of the values output by the command.
Parameters	Instance property (read-only)	Implementation defined collection	The parameters of the command.
ParameterSets	Instance property (read-only)	Implementation defined collection	Information about the parameter sets associated with the command.
Path	Instance property (read-only)	string	Gets the path of the application file.

In PowerShell, this type is System.Management.Automation.ApplicationInfo.

4.5.8 Cmdlet description type

This type encapsulates the state of a cmdlet. It has the following accessible members:

Member	Member Kind	Type	Purpose
CommandType	Instance property (read-only)	Implementation defined	Should compare equal with "Cmdlet".
DefaultParameterSet	Instance property (read-only)	Implementation defined	The default parameter set that is used if PowerShell cannot determine which parameter set to use based on the supplied arguments.
Definition	Instance property (read-only)	string	A description of the cmdlet.
HelpFile	Instance property (read-write)	string	The path to the Help file for the cmdlet.
ImplementingType	Instance property (read-write)	Implementation defined	The type that implements the cmdlet.
Module	Instance property (read-only)	Implementation defined (§4.5.12)	The module that defines this cmdlet.
ModuleName	Instance property (read-only)	string	The name of the module that defines the cmdlet.
Name	Instance property (read-only)	string	The name of the cmdlet.
Noun	Instance property (read-only)	string	The noun name of the cmdlet.
OutputType	Instance property (read-only)	Implementation defined collection	Specifies the types of the values output by the cmdlet.
Parameters	Instance property (read-only)	Implementation defined collection	The parameters of the cmdlet.
ParameterSets	Instance property (read-only)	Implementation defined collection	Information about the parameter sets associated with the cmdlet.
Verb	Instance property (read-only)	string	The verb name of the cmdlet.
PSSnapIn	Instance property (read-only)	Implementation defined	Windows PowerShell: Information about the Windows PowerShell snap-in that is used to register the cmdlet.

In PowerShell, this type is System.Management.Automation.CmdletInfo.

4.5.9 External script description type

This type encapsulates the state of an external script (one that is directly executable by PowerShell, but is not built-in). It has the following accessible members:

Member	Member Kind	Type	Purpose
CommandType	Instance property (read-only)	Implementation defined	Should compare equal with "ExternalScript".
Definition	Instance property (read-only)	string	A definition of the script.
Module	Instance property (read-only)	Implementation defined (§4.5.12)	The module that defines this script.
ModuleName	Instance property (read-only)	string	The name of the module that defines the script.
Name	Instance property (read-only)	string	The name of the script.
OriginalEncoding	Instance property (read-only)	Implementation defined	The original encoding used to convert the characters of the script to bytes.
OutputType	Instance property (read-only)	Implementation defined collection	Specifies the types of the values output by the script.
Parameters	Instance property (read-only)	Implementation defined collection	The parameters of the script.
ParameterSets	Instance property (read-only)	Implementation defined collection	Information about the parameter sets associated with the script.
Path	Instance property (read-only)	string	The path to the script file.
ScriptBlock	Instance property (read-only)	scriptblock	The external script.
ScriptContents	Instance property (read-only)	string	The original contents of the script.

In PowerShell, this type is System.Management.Automation.ExternalScriptInfo.

4.5.10 Function description type

This type encapsulates the state of a function. It has the following accessible members:

Member	Member Kind	Type	Purpose
CmdletBinding	Instance property (read-only)	bool	Indicates whether the function uses the same parameter binding that compiled cmdlets use (see §12.3.5).
CommandType	Instance property (read-only)	Implementation defined	Can be compared for equality with "Function" or "Filter" to see which of those this object represents.
DefaultParameterSet	Instance property (read-only)	string	Specifies the parameter set to use if that cannot be determined from the arguments (see §12.3.5).
Definition	Instance property (read-only)	string	A string version of ScriptBlock
Description	Instance property (read-write)	string	The description of the function.
Module	Instance property (read-only)	Implementation defined (§4.5.12)	The module from which this function was exported
ModuleName	Instance property (read-only)	string	The module in which this function was defined
Name	Instance property (read-only)	string	The name of the function
Options	Instance property (read-write)	Implementation defined	The scope options for the function (§3.5.4).
OutputType	Instance property (read-only)	Implementation defined collection	Specifies the types of the values output, in order (see §12.3.6).
Parameters	Instance property (read-only)	Implementation defined collection	Specifies the parameter names, in order. If the function acts like a cmdlet (see CmdletBinding above) the common parameters are included at the end of the collection.
ParameterSets	Instance property (read-only)	Implementation defined collection	Information about the parameter sets associated with the command. For each parameter, the result shows the parameter name and type, and indicates if the parameter is mandatory, by position or a switch parameter. If the function acts like a cmdlet (see CmdletBinding above) the common parameters are included at the end of the collection.
ScriptBlock	Instance property (read-only)	scriptblock (§4.3.6)	The body of the function

In PowerShell, this type is System.Management.Automation.FunctionInfo.

• CommandType has type System.Management.Automation.CommandTypes.
• Options has type System.Management.Automation.ScopedItemOptions.
• OutputType has type System.Collections.ObjectModel.ReadOnlyCollection``1[[System.Management.Automation.PSTypeName,System.Management.Automation]].
• Parameters has type System.Collections.Generic.Dictionary``2[[System.String,mscorlib],[System.Management.Automation.ParameterMetadata,System.Management.Automation]].
• ParameterSets has type System.Collections.ObjectModel.ReadOnlyCollection``1[[System.Management.Automation.CommandParameterSetInfo,System.Management.Automation]].
• Visibility has type System.Management.Automation.SessionStateEntryVisibility.
• PowerShell also has a property called Visibility.

4.5.11 Filter description type

This type encapsulates the state of a filter. It has the same set of accessible members as the function description type (§4.5.10).

In PowerShell, this type is System.Management.Automation.FilterInfo. It has the same set of properties as System.Management.Automation.FunctionInfo (§4.5.11).

4.5.12 Module description type

This type encapsulates the state of a module. It has the following accessible members:

Member	Member Kind	Type	Purpose
Description	Instance property (read-write)	string	The description of the module (set by the manifest)
ModuleType	Instance property (read-only)	Implementation defined	The type of the module (Manifest, Script, or Binary)
Name	Instance property (read-only)	string	The name of the module
Path	Instance property (read-only)	string	The module's path

In PowerShell, this type is System.Management.Automation.PSModuleInfo. The type of ModuleType is System.Management.Automation.ModuleType.

4.5.13 Custom object description type

This type encapsulates the state of a custom object. It has no accessible members.

In PowerShell, this type is System.Management.Automation.PSCustomObject. The cmdlets Import-Module and New-Object can generate an object of this type.

4.5.14 Command description type

The automatic variable $PsCmdlet is an object that represents the cmdlet or function being executed. The type of this object is implementation defined; it has the following accessible members:

Member	Member Kind	Type	Purpose
ParameterSetName	Instance property (read-only)	string	Name of the current parameter set (see ParameterSetName)
ShouldContinue	Instance method	Overloaded /bool	Requests confirmation of an operation from the user.
ShouldProcess	Instance method	Overloaded /bool	Requests confirmation from the user before an operation is performed.

In PowerShell, this type is System.Management.Automation.PSScriptCmdlet.

4.5.15 Error record description type

The automatic variable $Error contains a collection of error records that represent recent errors (§3.12). Although the type of this collection is unspecified, it does support subscripting to get access to individual error records.

In PowerShell, the collection type is System.Collections.ArrayList. The type of an individual error record in the collection is System.Management.Automation.ErrorRecord. This type has the following public properties:

• CategoryInfo - Gets information about the category of the error.
• ErrorDetails - Gets and sets more detailed error information, such as a replacement error message.
• Exception - Gets the exception that is associated with this error record.
• FullyQualifiedErrorId - Gets the fully qualified error identifier for this error record.
• InvocationInfo - Gets information about the command that was invoked when the error occurred.
• PipelineIterationInfo - Gets the status of the pipeline when this error record was created
• TargetObject - Gets the object that was being processed when the error occurred.

4.5.16 Enumerator description type

A number of variables are enumerators for collections (§4). The automatic variable $foreach is the enumerator created for any foreach statement. The automatic variable $input is the enumerator for a collection delivered to a function from the pipeline. The automatic variable $switch is the enumerator created for any switch statement.

The type of an enumerator is implementation defined; it has the following accessible members:

Member	Member Kind	Type	Purpose
Current	Instance property (read-only)	object	Gets the current element in the collection. If the enumerator is not currently positioned at an element of the collection, the behavior is implementation defined.
MoveNext	Instance method	None/bool	Advances the enumerator to the next element of the collection. Returns $true if the enumerator was successfully advanced to the next element; $false if the enumerator has passed the end of the collection.

In PowerShell, these members are defined in the interface System.IEnumerator, which is implemented by the types identified below. If the enumerator is not currently positioned at an element of the collection, an exception of type InvalidOperationException is raised. For $foreach, this type is System.Array+SZArrayEnumerator. For $input, this type is System.Collections.ArrayList+ArrayListEnumeratorSimple. For $switch, this type is System.Array+SZArrayEnumerator.

4.5.17 Directory description type

The cmdlet New-Item can create items of various kinds including FileSystem directories. The type of a directory description object is implementation defined; it has the following accessible members:

Member	Member Kind	Type	Purpose
Attributes	Instance property (read-write)	Implementation defined (§4.2.6.3)	Gets or sets one or more of the attributes of the directory object.
CreationTime	Instance property (read-write)	Implementation defined (§4.5.19)	Gets and sets the creation time of the directory object.
Extension	Instance property (read- only)	string	Gets the extension part of the directory name.
FullName	Instance property (read-only)	string	Gets the full path of the directory.
LastWriteTime	Instance property (read-write)	Implementation defined (§4.5.19)	Gets and sets the time when the directory was last written to.
Name	Instance property (read- only)	string	Gets the name of the directory.

In PowerShell, this type is System.IO.DirectoryInfo. The type of the Attributes property is System.IO.FileAttributes.

4.5.18 File description type

The cmdlet New-Item can create items of various kinds including FileSystem files. The type of a file description object is implementation defined; it has the following accessible members:

Member	Member Kind	Type	Purpose
Attributes	Instance property (read-write)	Implementation defined (§4.2.6.3)	Gets or sets one or more of the attributes of the file object.
BaseName	Instance property (read- only)	string	Gets the name of the file excluding the extension.
CreationTime	Instance property (read-write)	Implementation defined (§4.5.19)	Gets and sets the creation time of the file object.
Extension	Instance property (read- only)	string	Gets the extension part of the file name.
FullName	Instance property (read-only)	string	Gets the full path of the file.
LastWriteTime	Instance property (read-write)	Implementation defined (§4.5.19)	Gets and sets the time when the file was last written to.
Length	Instance property (read- only)	long	Gets the size of the file, in bytes.
Name	Instance property (read- only)	string	Gets the name of the file.
VersionInfo	Instance property (read- only)	Implementation defined	Windows PowerShell: This ScriptProperty returns a System.Diagnostics.FileVersionInfo for the file.

In PowerShell, this type is System.IO.FileInfo.

4.5.19 Date-Time description type

The type of a date-time description object is implementation defined; it has the following accessible members:

Member	Member Kind	Type	Purpose
Day	Instance property (read-only)	int	Gets the day component of the month represented by this instance.
Hour	Instance property (read-only)	int	Gets the hour component of the date represented by this instance.
Minute	Instance property (read-only)	int	Gets the minute component of the date represented by this instance.
Month	Instance property (read-only)	int	Gets the month component of the date represented by this instance.
Second	Instance property (read-only)	int	Gets the seconds component of the date represented by this instance.
Year	Instance property (read-only)	int	Gets the year component of the date represented by this instance.

An object of this type can be created by cmdlet Get-Date.

In PowerShell, this type is System.DateTime.

4.5.20 Group-Info description type

The type of a group-info description object is implementation defined; it has the following accessible members:

Member	Member Kind	Type	Purpose
Count	Instance property (read-only)	int	Gets the number of elements in the group.
Group	Instance property (read-only)	Implementation-defined collection	Gets the elements of the group.
Name	Instance property (read-only)	string	Gets the name of the group.
Values	Instance property (read-only)	Implementation-defined collection	Gets the values of the elements of the group.

An object of this type can be created by cmdlet Group-Object.

In PowerShell, this type is Microsoft.PowerShell.Commands.GroupInfo.

4.5.21 Generic-Measure-Info description type

The type of a generic-measure-info description object is implementation defined; it has the following accessible members:

Member	Member Kind	Type	Purpose
Average	Instance property (read-only)	double	Gets the average of the values of the properties that are measured.
Count	Instance property (read-only)	int	Gets the number of objects with the specified properties.
Maximum	Instance property (read-only)	double	Gets the maximum value of the specified properties.
Minimum	Instance property (read-only)	double	Gets the minimum value of the specified properties.
Property	Instance property (read-only)	string	Gets the property to be measured.
Sum	Instance property (read-only)	double	Gets the sum of the values of the specified properties.

An object of this type can be created by cmdlet Measure-Object.

In PowerShell, this type is Microsoft.PowerShell.Commands.GenericMeasureInfo.

4.5.22 Text-Measure-Info description type

The type of a text-info description object is implementation defined; it has the following accessible members:

Member	Member Kind	Type	Purpose
Characters	Instance property (read-only)	int	Gets the number of characters in the target object.
Lines	Instance property (read-only)	int	Gets the number of lines in the target object.
Property	Instance property (read-only)	string	Gets the property to be measured.
Words	Instance property (read-only)	int	Gets the number of words in the target object.

An object of this type can be created by cmdlet Measure-Object.

In PowerShell, this type is Microsoft.PowerShell.Commands.TextMeasureInfo.

4.5.23 Credential type

A credential object can then be used in various security operations. The type of a credential object is implementation defined; it has the following accessible members:

Member	Member Kind	Type	Purpose
Password	Instance property (read-only)	Implementation defined	Gets the password.
UserName	Instance property (read-only)	string	Gets the username.

An object of this type can be created by cmdlet Get-Credential.

In PowerShell, this type is System.Management.Automation.PSCredential.

4.5.24 Method designator type

The type of a method designator is implementation defined; it has the following accessible members:

Member	Member Kind	Type	Purpose
Invoke	Instance method	object/variable number and type	Takes a variable number of arguments, and indirectly calls the method referred to by the parent method designator, passing in the arguments.

An object of this type can be created by an invocation-expression (§7.1.3).

In PowerShell, this type is System.Management.Automation.PSMethod.

4.5.25 Member definition type

This type encapsulates the definition of a member. It has the following accessible members:

Member	Member Kind	Type	Purpose
Definition	Instance property (read-only)	string	Gets the definition of the member.
MemberType	Instance property (read-only)	Implementation defined	Gets the PowerShell type of the member.
Name	Instance property (read-only)	string	Gets the name of the member.
TypeName	Instance property (read-only)	string	Gets the type name of the member.

In PowerShell, this type is Microsoft.PowerShell.Commands.MemberDefinition.

4.6 Type extension and adaptation

A PowerShell implementation includes a family of core types (which are documented in this chapter) that each contain their own set of base members. Those members can be methods or properties, and they can be instance or static members. For example, the base members of the type string (§4.3.1) are the instance property Length and the instance methods ToLower and ToUpper.

When an object is created, it contains all the instance properties of that object's type, and the instance methods of that type can be called on that object. An object may be customized via the addition of instance members at runtime. The result is called a custom object. Any members added to an instance exist only for the life of that instance; other instances of the same core type are unaffected.

The base member set of a type can be augmented by the addition of the following kinds of members:

• adapted members, via the Extended Type System (ETS), most details of which are unspecified.
• extended members, via the cmdlet Add-Member.

In PowerShell, extended members can also be added via types.ps1xml files. Adapted and extended members are collectively called synthetic members.

The ETS adds the following members to all PowerShell objects: psbase, psadapted, psextended, and pstypenames. See the Force and View parameters in the cmdlet Get-Member for more information on these members.

An instance member may hide an extended and/or adapted member of the same name, and an extended member may hide an adapted member. In such cases, the member sets psadapted and psextended can be used to access those hidden members.

If a types.ps1xml specifies a member called Supports, obj.psextended provides access to just that member and not to a member added via Add-Member.

There are three ways create a custom object having a new member M:

1. This approach can be used to add one or more NoteProperty members.

   $x = New-Object PSObject -Property @{M = 123}
   

2. This approach can be used to add NoteProperty or ScriptMethod members.

   $x = New-Module -AsCustomObject {$M = 123 ; Export-ModuleMember --Variable M}
   

3. This approach can be used to add any kind of member.

   $x = New-Object PSObject
   Add-Member -InputObject $x -Name M -MemberType NoteProperty -Value 123
   

PSObject is the base type of all PowerShell types.