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Type query for a result of a function call #6239
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Seems that no. It would be great to do something like:
declare var do: (arg: string) => number let a: typeof do // a now has (arg: string) => number type let b: typeof do() // b now has number typeThis comment is related: #2710 (comment)
Duplicate of #4233?
I have also encountered this problem many times.
What would be the inferred type in the following situation?
function fn<a>(value: a) : { value: a; } { return { value: value }; } let a: typeof fn;
If the answer is
{value: {}}(assuming the current state of affairs) then such feature is useless.Daniel Rosenwasser (@DanielRosenwasser), how feasible is it to allow variables to hold
unresolvedits own declared (not from the context) type parameters?Might be related #5959
I think answer should be an error about required type argument, and developer should write
let a: typeof fn<number>()
to get
{value: number}Artur Eshenbrener (@Strate)
this is pure syntax sugar overlet b = fn<number>(); let a : typeof b;
if this is what you are looking for then it might be better phrased as "Type query for a result of a function call"
You are right, I'm gonna to change the caption :)
- changed the title
[-]Type query for function's result[/-][+]Type query for a result of a function call[/+]on Dec 25, 2015 I'm wondering how this would handle overloaded functions? I guess one must pass in the type of the arguments to let it overload correctly the return type.
function f(a: string): string; function f(a: string, b: number): boolean; function f(a: string, b?: string | number, c?: string): boolean | string { return true; } typeof f(string, number) // boolean
Isn't ellipses
...a better syntax for not overloaded functions? Because onlyf()(no arguments) doesn't corresponds to the function signaturef(a: string)(with one argument).function f(a: string): boolean; typeof f(...) // boolean
Tingan Ho (@tinganho) #4233 takes care of that - just use any valid expression - like
typeof f("", 0)Proposal + implementation that covers this: #6606
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on Jun 19, 2018
Is it possible to use
typeoftype query operator to get function's return type?