Support type wildcards (_)

[michaeljklein]

Problem

Currently,

1. When using turbofish with multiple arguments, e.g.

foo<A, B, 3, 12>

4. When the return type is underconstrained, e.g. when deserializing from an array of Field's:

let deserialized: Vec<MyStruct> = input.deserialize();

(i.e. collect::<Vec<_>>())

This can require a lot of duplication when functions/traits have several generic arguments and makes the resulting code more fragile.

Happy Case

Support a type wildcard (_) that's equivalent to an unbound type variable and errors at monomorphization if still unbound:

foo<_, _, 3, 12>

let deserialized: Vec<_> = input.deserialize();

Project Impact

Nice-to-have

Impact Context

No response

Workaround

Yes

Workaround Description

Specify all of the arguments and types explicitly

Additional Context

No response

Would you like to submit a PR for this Issue?

None

Support Needs

No response

[TomAFrench]

See #4664