Access Modifiers (C# Programming Guide)

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08/20/2024

All types and type members have an accessibility level. The accessibility level controls whether they can be used from other code in your assembly or other assemblies. An assembly is a .dll or .exe created by compiling one or more .cs files in a single compilation. Use the following access modifiers to specify the accessibility of a type or member when you declare it:

public: Code in any assembly can access this type or member. The accessibility level of the containing type controls the accessibility level of public members of the type.
private: Only code declared in the same class or struct can access this member.
protected: Only code in the same class or in a derived class can access this type or member.
internal: Only code in the same assembly can access this type or member.
protected internal: Only code in the same assembly or in a derived class in another assembly can access this type or member.
private protected: Only code in the same assembly and in the same class or a derived class can access the type or member.
file: Only code in the same file can access the type or member.

The record modifier on a type causes the compiler to synthesize extra members. The record modifier doesn't affect the default accessibility for either a record class or a record struct.

Summary table

Caller's location	`public`	`protected internal`	`protected`	`internal`	`private protected`	`private`	`file`
Within the file	✔️️	✔️	✔️	✔️	✔️	✔️	✔️
Within the class	✔️️	✔️	✔️	✔️	✔️	✔️	❌
Derived class (same assembly)	✔️	✔️	✔️	✔️	✔️	❌	❌
Non-derived class (same assembly)	✔️	✔️	❌	✔️	❌	❌	❌
Derived class (different assembly)	✔️	✔️	✔️	❌	❌	❌	❌
Non-derived class (different assembly)	✔️	❌	❌	❌	❌	❌	❌

The following examples demonstrate how to specify access modifiers on a type and member:

public class Bicycle
{
    public void Pedal() { }
}

Not all access modifiers are valid for all types or members in all contexts. In some cases, the accessibility of the containing type constrains the accessibility of its members.

Multiple declarations of a partial class or partial member must have the same accessibility. If one declaration of the partial class or member doesn't include an access modifier, the other declarations can't declare an access modifier. The compiler generates an error if multiple declarations for the partial class or method declare different accessibilities.

Class and struct accessibility

Classes and structs declared directly within a namespace (aren't nested within other classes or structs) can have public, internal or file access. internal is the default if no access modifier is specified.

Struct members, including nested classes and structs, can be declared public, internal, or private. Class members, including nested classes and structs, can be public, protected internal, protected, internal, private protected, or private. Class and struct members, including nested classes and structs, have private access by default.

Derived classes can't have greater accessibility than their base types. You can't declare a public class B that derives from an internal class A. If allowed, it would have the effect of making A public, because all protected or internal members of A are accessible from the derived class.

You can enable specific other assemblies to access your internal types by using the InternalsVisibleToAttribute. For more information, see Friend Assemblies.

Other types

Interfaces declared directly within a namespace can be public or internal and, just like classes and structs, interfaces default to internal access. Interface members are public by default because the purpose of an interface is to enable other types to access a class or struct. Interface member declarations might include any access modifier. You use access modifiers on interface members to provide a common implementation needed by all implementors of an interface.

A delegate type declared directly in a namespace has internal access by default.

For more information about access modifiers, see the Accessibility Levels page.

Member accessibility

Members of a class or struct (including nested classes and structs) can be declared with any of the six types of access. Struct members can't be declared as protected, protected internal, or private protected because structs don't support inheritance.

Normally, the accessibility of a member isn't greater than the accessibility of the type that contains it. However, a public member of an internal class might be accessible from outside the assembly if the member implements interface methods or overrides virtual methods that are defined in a public base class.

The type of any member field, property, or event must be at least as accessible as the member itself. Similarly, the return type and the parameter types of any method, indexer, or delegate must be at least as accessible as the member itself. For example, you can't have a public method M that returns a class C unless C is also public. Likewise, you can't have a protected property of type A if A is declared as private.

User-defined operators must always be declared as public and static. For more information, see Operator overloading.

To set the access level for a class or struct member, add the appropriate keyword to the member declaration, as shown in the following example.

// public class:
public class Tricycle
{
    // protected method:
    protected void Pedal() { }

    // private field:
    private int _wheels = 3;

    // protected internal property:
    protected internal int Wheels
    {
        get { return _wheels; }
    }
}

Finalizers can't have accessibility modifiers. Members of an enum type are always public, and no access modifiers can be applied.

The file access modifier is allowed only on top-level (non-nested) type declarations.

C# language specification

For more information, see the C# Language Specification. The language specification is the definitive source for C# syntax and usage.

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