"Implicit" Attribute for generic parameters

[MkazemAkhgary]

Here is the lightbulb! no new syntax, no breaking change. no compiler option.

introduce "Implicit" attribute for generic parameters so that compiler will automatically infer generic type arguments when method is called.

void Foo<TSource, [Implicit] T>(TSource x) where TSource : IList<T>
{
}

this will let compiler know that we intend to infer T implicitly. because its already some where hidden in input! (in this case IList<T>) so as an example, following call becomes valid

Foo(new List<int>());

This special attribute must also cause compile time error if marked generic parameter is not found anywhere in input, for example

void Foo<[Implicit] T>() // Error: no usage of T found in method signature.
{
}

[orthoxerox]

I think implicit generic parameters are being prototyped in the concepts fork.

cc @MattWindsor91

[MattWindsor91]

@orthoxerox Sadly only for concept parameters.

Having it work for normal type parameters would be a logical extension and make the concepts version feel more orthogonal and less weird, but I genuinely don’t know how much would this be useful outside of concepts as I haven’t looked into it.

[gafter]

@agocke is investigating extending type inference to take constraints into account.

[alrz]

extending type inference

What is the scope of this feature? would we be able to consider other improvements for type inference? for instance: #92, #877, #281, etc