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C# 7.x: private protected access modifier #215

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Sep 7, 2022
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C# 7.x: private protected access modifier #215

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3728abf
Update basic-concepts.md
RexJaeschke Jan 25, 2021
ca1e44d
Update namespaces.md
RexJaeschke Jan 25, 2021
a9c2171
Update structs.md
RexJaeschke Jan 25, 2021
52c0490
Update unsafe-code.md
RexJaeschke Jan 25, 2021
de5df83
Update classes.md
RexJaeschke Jan 25, 2021
36859cc
Update standard/classes.md
gafter Jun 8, 2022
7d39a45
Address review comments for private protected
jskeet Jul 26, 2022
1551565
Fixes for fixed buffer accessibility
jskeet Sep 7, 2022
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10 changes: 6 additions & 4 deletions standard/basic-concepts.md
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Expand Up @@ -221,15 +221,16 @@ The ***declared accessibility*** of a member can be one of the following:
- Protected, which is selected by including a `protected` modifier in the member declaration. The intuitive meaning of `protected` is “access limited to the containing class or types derived from the containing class”.
- Internal, which is selected by including an `internal` modifier in the member declaration. The intuitive meaning of `internal` is “access limited to this assembly”.
- Protected internal, which is selected by including both a `protected` and an `internal` modifier in the member declaration. The intuitive meaning of `protected internal` is “accessible within this assembly as well as types derived from the containing class”.
- Private protected, which is selected by including both a `private` and a `protected` modifier in the member declaration. The intuitive meaning of `private protected` is "accessible within this assembly by the containing class and types derived from the containing class."
- Private, which is selected by including a `private` modifier in the member declaration. The intuitive meaning of `private` is “access limited to the containing type”.

Depending on the context in which a member declaration takes place, only certain types of declared accessibility are permitted. Furthermore, when a member declaration does not include any access modifiers, the context in which the declaration takes place determines the default declared accessibility.

- Namespaces implicitly have `public` declared accessibility. No access modifiers are allowed on namespace declarations.
- Types declared directly in compilation units or namespaces (as opposed to within other types) can have `public` or `internal` declared accessibility and default to `internal` declared accessibility.
- Class members can have any of the five kinds of declared accessibility and default to `private` declared accessibility.
> *Note*: A type declared as a member of a class can have any of the five kinds of declared accessibility, whereas a type declared as a member of a namespace can have only `public` or `internal` declared accessibility. *end note*
- Struct members can have `public`, `internal`, or `private` declared accessibility and default to `private` declared accessibility because structs are implicitly sealed. Struct members introduced in a `struct` (that is, not inherited by that struct) cannot have `protected` or `protected internal` declared accessibility.
- Class members can have any of the permitted kinds of declared accessibility and default to `private` declared accessibility.
> *Note*: A type declared as a member of a class can have any of the permitted kinds of declared accessibility, whereas a type declared as a member of a namespace can have only `public` or `internal` declared accessibility. *end note*
- Struct members can have `public`, `internal`, or `private` declared accessibility and default to `private` declared accessibility because structs are implicitly sealed. Struct members introduced in a `struct` (that is, not inherited by that struct) cannot have `protected`, `protected internal`, or `private protected` declared accessibility.
> *Note*: A type declared as a member of a struct can have `public`, `internal`, or `private` declared accessibility, whereas a type declared as a member of a namespace can have only `public` or `internal` declared accessibility. *end note*
- Interface members implicitly have `public` declared accessibility. No access modifiers are allowed on interface member declarations.
- Enumeration members implicitly have `public` declared accessibility. No access modifiers are allowed on enumeration member declarations.
Expand All @@ -253,6 +254,7 @@ The accessibility domain of a nested member `M` declared in a type `T` within

- If the declared accessibility of `M` is `public`, the accessibility domain of `M` is the accessibility domain of `T`.
- If the declared accessibility of `M` is `protected internal`, let `D` be the union of the program text of `P` and the program text of any type derived from `T`, which is declared outside `P`. The accessibility domain of `M` is the intersection of the accessibility domain of `T` with `D`.
- If the declared accessibility of `M` is `private protected`, let `D` be the intersection of the program text of `P` and the program text of `T` and any type derived from `T`. The accessibility domain of `M` is the intersection of the accessibility domain of `T` with `D`.
- If the declared accessibility of `M` is `protected`, let `D` be the union of the program text of `T`and the program text of any type derived from `T`. The accessibility domain of `M` is the intersection of the accessibility domain of `T` with `D`.
- If the declared accessibility of `M` is `internal`, the accessibility domain of `M` is the intersection of the accessibility domain of `T` with the program text of `P`.
- If the declared accessibility of `M` is `private`, the accessibility domain of `M` is the program text of `T`.
Expand Down Expand Up @@ -348,7 +350,7 @@ As described in [§7.4](basic-concepts.md#74-members), all members of a base cla

### 7.5.4 Protected access

When a `protected` instance member is accessed outside the program text of the class in which it is declared, and when a `protected internal` instance member is accessed outside the program text of the program in which it is declared, the access shall take place within a class declaration that derives from the class in which it is declared. Furthermore, the access is required to take place *through* an instance of that derived class type or a class type constructed from it. This restriction prevents one derived class from accessing protected members of other derived classes, even when the members are inherited from the same base class.
When a `protected` or `private protected` instance member is accessed outside the program text of the class in which it is declared, and when a `protected internal` instance member is accessed outside the program text of the program in which it is declared, the access shall take place within a class declaration that derives from the class in which it is declared. Furthermore, the access is required to take place *through* an instance of that derived class type or a class type constructed from it. This restriction prevents one derived class from accessing protected members of other derived classes, even when the members are inherited from the same base class.

Let `B` be a base class that declares a protected instance member `M`, and let `D` be a class that derives from `B`. Within the *class_body* of `D`, access to `M` can take one of the following forms:

Expand Down
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