Create Function Type (TypeScript Interface)

Question

I need to make a function type that tells me what the type must be for the second value based on the first value

  type BType = number | string | array
  enum AEnum = { number = "number" , string : "string" , array : "array"} 

  const fc = (a : AEnum , b : BType)=>{ 
   //...
  }

What I need is that when a = AEnum.array, then b must be array, or an error should be shown

How can I make something like this ??

Please provide a self-contained minimal reproducible example that clearly demonstrates the issue you are facing. Ideally I could paste such code into a standalone IDE and immediately get to work solving the problem without first needing to re-create it. So there should be no pseudocode, typos, unrelated errors, or undeclared types or values. — jcalz
– jcalz, Commented Jul 10, 2022 at 15:56

Matthieu Riegler · Accepted Answer · 2022-07-10 15:58:50Z

2

Just overload the function !

type BType = number | string | []
enum AEnum { number = "number", string = "string", array = "array" }

function foo(a: AEnum.number, b: number): unknown;
function foo(a: AEnum.string, b: string): unknown;
function foo(a: AEnum.array, b: []): unknown;
function foo(a: AEnum, b: BType): unknown {
    return void;
}

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answered Jul 10, 2022 at 15:58

Matthieu Riegler

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