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f#ref-struct

How to define a ref struct in F# in .NET Standard 2.0?

When F# 4.5 was announced, it was stated that:

The F# feature set is comprised of

  • [...]

  • The ability to produce IsByRefLike structs (examples of such structs: Span<'T>and ReadOnlySpan<'T>).

How to "produce" these types? I tried the [<IsByRefLike>] attribute but is was not found in .NET Standard 2.0.

Solution

  • Starting with .NET SDK 6.0.200 (available in Visual Studio 2022 17.1), the F# compiler recognizes user-defined IsByRefLikeAttributes. The following code will transparently enable defining ref structs on .NET Standard 2.0 as well as later frameworks:

    #if NETSTANDARD2_0
namespace System.Runtime.CompilerServices

open System

[<Sealed; AttributeUsage(AttributeTargets.Struct)>]
type IsByrefLikeAttribute() = inherit Attribute()
#endif

namespace MyLibrary

open System
open System.Runtime.CompilerServices

[<IsByRefLike>]
type MyRefStruct(span: Span<int>) = struct end