Idea: Type Unpackers for Function Parameters

Because of TypeScript 2.8 Conditional Types, we can now do the following:

type Param0<Func> = Func extends (a: infer T, ...args: any[]) => any
	? T
	: never;
type T0 = Param0<() => void>; // {}
type T1 = Param0<(a: number) => void>; // number
type T2 = Param0<(a: string[]) => void>; // string[]

Issue for discussion!

Questions:

• Naming scheme?
• Multiple Parameter Unpacks at the same time?

See also ReturnType<Func>

[pelotom]

On second thought you may be right about performance being a concern… I agree it might be better to play it safe.

[pelotom]

ArgumentsType seems more consistent, in line with arguments as well as (...args: any[]).

Parameters are the declared inputs of a function signature, arguments are the runtime objects passed to a function:

https://stackoverflow.com/questions/156767/whats-the-difference-between-an-argument-and-a-parameter

@pelotom Is there a performance concern re: unpacking the whole array by default? If people are mostly going to access a single parameter, maybe we should consider that?

I really doubt there’s much performance difference.