Native Integer Metadata

The following describes the representation of native integers in metadata.

NativeIntegerAttribute

Type references are annotated in metadata with a NativeIntegerAttribute.

namespace System.Runtime.CompilerServices
{
    [AttributeUsage(
        AttributeTargets.Class |
        AttributeTargets.Event |
        AttributeTargets.Field |
        AttributeTargets.GenericParameter |
        AttributeTargets.Parameter |
        AttributeTargets.Property |
        AttributeTargets.ReturnValue,
        AllowMultiple = false,
        Inherited = false)]
    public sealed class NativeIntegerAttribute : Attribute
    {
        public NativeIntegerAttribute()
        {
            TransformFlags = new[] { true };
        }
        public NativeIntegerAttribute(bool[] flags)
        {
            TransformFlags = flags;
        }
        public readonly bool[] TransformFlags;
    }
}

The NativeIntegerAttribute type is for compiler use only - it is not permitted in source. The type declaration is synthesized by the compiler if not already included in the compilation.

Each type reference in metadata may have an associated NativeIntegerAttribute with a bool[] where each bool represents whether the associated type is a native integer (nint or nuint in C#) or the underlying type (System.IntPtr or System.UIntPtr). Custom modifiers associated with the type reference are ignored.

A type reference may have at most one NativeIntegerAttribute. The attribute is not inherited.

The bool[] is constructed as follows:

• System.IntPtr, System.UIntPtr: true if the type represents a native integer; false otherwise
• Generic type: the representation of the type arguments in order including containing types
• Tuple: the representation of the underlying constructed type
• Array: the representation of the element type
• Pointer type: the representation of the pointed at type
• Function pointer type: the representation of the return type followed by the parameter types in order
• Other: none

Given the construction above, the number of elements in the bool[] matches the number of references to System.IntPtr and System.UIntPtr in the type.

Optimizations

If the bool[] is empty, the NativeIntegerAttribute is omitted.

If the bool[] contains a single true value, the NativeIntegerAttribute uses the parameter-less constructor.

Examples

System.IntPtr A;         // System.IntPtr A
nint B;                  // [NativeInteger] System.IntPtr B
IEnumerable<nuint> C     // [NativeInteger] System.Collections.Generic.IEnumerable C
(System.IntPtr, nint) D; // [NativeInteger(new[] { false, true })] System.ValueTuple D