Delegates as structs in C#

StructFun.cs

var freeVar = 100;
Func<string, int> length = x => x.Length + freeVar;

var f = new Fun<string, int>(length);
var r = f.Invoke("Hello");
Console.WriteLine(r);      // 105

public readonly unsafe struct Fun<A>
{
    readonly object? self;
    readonly IntPtr func;

    public Fun(object? self, IntPtr func) =>
        (this.self, this.func) = (self, func);

    public Fun(Func<A> function)
        : this(function.Target, function.Method.MethodHandle.GetFunctionPointer())
    { }

    public A Invoke()
    {
        var f = (delegate*<object?, A>)func;
        return f(self);
    }
}

public readonly unsafe struct Fun<A, B>
{
    readonly object? self;
    readonly IntPtr func;

    public Fun(object? self, IntPtr func) =>
        (this.self, this.func) = (self, func);

    public Fun(Func<A, B> function)
        : this(function.Target, function.Method.MethodHandle.GetFunctionPointer())
    { }

    public B Invoke(in A value)
    {
        var f = (delegate*<object?, A, B>)func;
        return f(self, value);
    }
}