Question

TypeBuilder.GetMethod allows you to get a method on a generic type closed by a TypeBuilder so it lets me to the following:

TypeBuilder tb = ....
// this would throw a NotSupportedException : 
// var ec = typeof(EqualityComparer<>).
//     MakeGenericType(tb).GetMethod("get_Default");

// this works:
var ec = TypeBuilder.GetMethod(tb, typeof(EqualityComparer<>).
    GetMethod("get_Default");

What doesn’t work (and I can’t figure out how to make it work yet) is this:

Type collectionOf = typeof(ICollection<>).MakeGenericType(tb);
// throws: 'Type must be a type provided by the runtime. 
// Parameter name: types'
var colEc = TypeBuilder.GetMethod(collectionOf, typeof(EqualityComparer<>).
    GetMethod("get_Default");
// throws NotSupportedException
colEc = typeof(EqualityComparer<>).MakeGenericType(collectionOf).
    GetMethod("get_Default");

Anyone know the answer (I hope it’s 42)…?

Answer 1

It’s not completely clear to me what you’re trying to do (it looks like you’re missing some parentheses, among other issues), but if you’re trying to get a MethodInfo for EqualityComparer<ICollection<YourType>>.get_Default, this works for me:

var ab = AppDomain.CurrentDomain.DefineDynamicAssembly(new AssemblyName("test"),
             AssemblyBuilderAccess.Run);
var mb = ab.DefineDynamicModule("test");
var tb = mb.DefineType("TestType");

var ico = typeof(ICollection<>);
var eq = typeof(EqualityComparer<>);

var m = TypeBuilder.GetMethod(eq.MakeGenericType(ico.MakeGenericType(tb)), eq.GetMethod("get_Default"));