Cannot compile default generic values in C#

[MikaelMayer]

If you compile the following program:

datatype KeyValues<T> = Store(underlying: map<string, T> := map[])

function method CreateStore<T>(): (r: KeyValues<T>) {
  Store()
}

You'll get a compilation error:

Errors compiling program into csharpcompilerbug
(4886,69): error CS0246: The type or namespace name 'T' could not be found (are you missing a using directive or an assembly reference?)

(4886,36): error CS1503: Argument 1: cannot convert from 'Dafny.Map<Dafny.ISequence<char>, T>' to 'Dafny.IMap<Dafny.ISequence<char>, __T>'

This comes from the fact that Dafny did not infer the type parameter of the default variable to be the same T, and there is no way to provide this in the constructor as far as I know.

The workaround is to explicit the default value for now:

datatype KeyValues<T> = Store(underlying: map<string, T> := map[])

function method CreateStore<T>(): (r: KeyValues<T>) {
  var x: map<string, T> := map[];
  Store(x)
}