MethodImplAttributes MethodImplAttributes MethodImplAttributes MethodImplAttributes Enum


Specifies flags for the attributes of a method implementation.

This enumeration has a FlagsAttribute attribute that allows a bitwise combination of its member values.

This API supports the product infrastructure and is not intended to be used directly from your code.

public enum class MethodImplAttributes
public enum MethodImplAttributes
type MethodImplAttributes = 
Public Enum MethodImplAttributes


AggressiveInlining AggressiveInlining AggressiveInlining AggressiveInlining 256

Specifies that the method should be inlined wherever possible.

AggressiveOptimization AggressiveOptimization AggressiveOptimization AggressiveOptimization 512

Specifies that the method should be optimized whenever possible.

CodeTypeMask CodeTypeMask CodeTypeMask CodeTypeMask 3

Specifies flags about code type.

ForwardRef ForwardRef ForwardRef ForwardRef 16

Specifies that the method is not defined.


Specifies that the method implementation is in Microsoft intermediate language (MSIL).

InternalCall InternalCall InternalCall InternalCall 4096

Specifies an internal call.

Managed Managed Managed Managed 0

Specifies that the method is implemented in managed code.

ManagedMask ManagedMask ManagedMask ManagedMask 4

Specifies whether the method is implemented in managed or unmanaged code.

MaxMethodImplVal MaxMethodImplVal MaxMethodImplVal MaxMethodImplVal 65535

Specifies a range check value.

Native Native Native Native 1

Specifies that the method implementation is native.

NoInlining NoInlining NoInlining NoInlining 8

Specifies that the method cannot be inlined.

NoOptimization NoOptimization NoOptimization NoOptimization 64

Specifies that the method is not optimized by the just-in-time (JIT) compiler or by native code generation (see Ngen.exe) when debugging possible code generation problems.


Specifies that the method implementation is in Optimized Intermediate Language (OPTIL).

PreserveSig PreserveSig PreserveSig PreserveSig 128

Specifies that the method signature is exported exactly as declared.

Runtime Runtime Runtime Runtime 3

Specifies that the method implementation is provided by the runtime.

SecurityMitigations SecurityMitigations SecurityMitigations SecurityMitigations 1024

Specifies that the JIT compiler should look for security mitigation attributes, such as the user-defined System.Runtime.CompilerServices.SecurityMitigationsAttribute. If found, the JIT compiler applies any related security mitigations. Available starting with .NET Framework 4.8.

Synchronized Synchronized Synchronized Synchronized 32

Specifies that the method is single-threaded through the body. Static methods (Shared in Visual Basic) lock on the type, whereas instance methods lock on the instance. You can also use the C# lock statement or the Visual Basic SyncLock statement for this purpose.

Unmanaged Unmanaged Unmanaged Unmanaged 4

Specifies that the method is implemented in unmanaged code.


The attributes are combined using the bitwise OR operation as follows:

Code implementation masks:

  • CodeTypeMask

  • IL

  • Native


  • Runtime

Managed masks:

  • ManagedMask

  • Unmanaged

  • Managed

Implementation information and interop masks:

  • ForwardRef

  • PreserveSig

  • InternalCall

  • Synchronized

  • NoInlining

  • NoOptimization

  • MaxMethodImplVal

  • SecurityMitigations (Available starting with .NET Framework 4.8.)


Locking on the instance or on the type, as with the Synchronized flag, is not recommended for public types, because code other than your own can take locks on public types and instances. This might cause deadlocks or other synchronization problems.

Applies to

See also