> ## Documentation Index
> Fetch the complete documentation index at: https://docs.syntblaze.com/llms.txt
> Use this file to discover all available pages before exploring further.
# C# Private Protected Field
The `private protected` access modifier restricts member visibility to the containing class and types derived from that class, strictly provided they reside within the same assembly. Introduced in C# 7.2, it acts as a logical AND operation between the `internal` (same assembly) and `protected` (derived types) modifiers, making it more restrictive than either modifier individually.
```csharp theme={"dark"}
public class BaseClass
{
private protected int _stateValue;
}
```
## Access Mechanics
To access a `private protected` field, the consuming type must satisfy **both** of the following conditions simultaneously:
1. **Inheritance:** The consuming type must inherit from the class declaring the field.
2. **Location:** The consuming type must be compiled into the exact same assembly as the declaring class.
This contrasts directly with the `protected internal` modifier, which functions as a logical OR operation (accessible if derived *or* in the same assembly).
## Compilation Boundaries
The following code block demonstrates the strict compilation boundaries enforced by the `private protected` modifier across different scopes and assemblies.
```csharp theme={"dark"}
// =========================================
// Assembly A
// =========================================
public class BaseClass
{
private protected int _coreField;
}
public class DerivedInSameAssembly : BaseClass
{
public void MutateField()
{
// VALID: Type is derived AND resides in Assembly A.
_coreField = 42;
}
}
public class NonDerivedInSameAssembly
{
public void AttemptMutation(BaseClass instance)
{
// ERROR CS0122: '_coreField' is inaccessible due to its protection level.
// Fails condition: Not a derived type.
instance._coreField = 42;
}
}
// =========================================
// Assembly B (References Assembly A)
// =========================================
public class DerivedInDifferentAssembly : BaseClass
{
public void AttemptMutation()
{
// ERROR CS0122: '_coreField' is inaccessible due to its protection level.
// Fails condition: Resides in Assembly B, not Assembly A.
_coreField = 42;
}
}
```
## CLR Implementation
At the Common Intermediate Language (CIL) level, the `private protected` modifier is represented by the `famandassem` accessibility attribute. This instructs the Common Language Runtime (CLR) to enforce the intersection of `family` (protected) and `assembly` (internal) visibility rules during Just-In-Time (JIT) compilation and execution.
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