give _ToProc#to_proc a return type

[ParadoxV5]

I don’t know what purpose are the interfaces in builtin.rbs, but I do use them for implicit conversion. The return of _ToProc#to_proc, however, is untyped and I cannot see why. This is the contract for implicit conversion to a block when prefixed with & (an_array.map(&a_to_proc)).

[ParadoxV5]

[Discussion] just typing it as Proc isn’t very useful since RBS has “Proc type”s.

• We could make it _ToProc[^(specific_arg_types) -> specific_return type] so one can specify the resulting Proc’s contract.
• The current solution is to write a custom interface that defines the desired contract: def to_proc: ^(specific_arg_types) -> specific_return type.

Regardless of which bullet point to adopt, _ToProc#to_proc doesn’t make sense not having a return type – unless _ToProc shouldn’t exist fundamentally.

[soutaro]

Thanks @ParadoxV5,

Having Proc is an improvement while it doesn't make much sense, as you said. It makes sense that passing a proc type to the type parameter, but still it's not very useful because we don't have something to express the constraints on the arguments of a proc/method.