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Value Types and Reference Types

  • Artykuł

A data type is a value type if it holds the data within its own memory allocation. A reference type contains a pointer to another memory location that holds the data.

Value Types

Value types include the following:

  • All numeric data types

  • Boolean, Char, and Date

  • All structures, even if their members are reference types

  • Enumerations, since their underlying type is always SByte, Short, Integer, Long, Byte, UShort, UInteger, or ULong

Reference Types

Reference types include the following:

  • String

  • All arrays, even if their elements are value types

  • Class types, such as Form

  • Delegates

Elements That Are Not Types

The following programming elements do not qualify as types, because you cannot specify any of them as a data type for a declared element:

  • Namespaces

  • Modules

  • Events

  • Properties and procedures

  • Variables, constants, and fields

Working with the Object Data Type

You can assign either a reference type or a value type to a variable of the Object data type. An Object variable always holds a pointer to the data, never the data itself. However, if you assign a value type to an Object variable, it behaves as if it holds its own data. For more information, see Object Data Type.

You can find out whether an Object variable is acting as a reference type or a value type by passing it to the IsReference method on the Information class in the Microsoft.VisualBasic namespace. Information.IsReference returns True if the content of the Object variable represents a reference type.

See Also

Concepts

Data Types Are .NET Framework Types

Efficient Use of Data Types

Reference

Object Data Type

Other Resources

Type Conversions in Visual Basic

Structures: Your Own Data Types