Theo's Typesafe Cult•3y ago

Help me type this function

I have a function that takes in an input function and returns another function who's input is the same type as the function passed into it.

function Foo<T>(callback: (input?: T) => void){
  return async function(input?: T) => {
    //...
  }
}

function Foo<T>(callback: (input?: T) => void){
  return async function(input?: T) => {
    //...
  }
}

However, I want the return function type to either require or not require input based on if callback has a parameter or not. How would I do this?

4 Replies

CaptainStarz•3y ago

something like this probably https://www.typescriptlang.org/play?ts=4.8.4#code/GYVwdgxgLglg9mABAdwE4EMAOBhARgHmwCFEBTADylLABMBnRACgDpX1UBzOgLkXTACeAbQC6ASkQBeAHx9B0xhFy9iYlSQDeAKES7EqUlBCokoSLAQoMmTKRp4WbTj0QAFdugC2h0qjqEiaTVEACVDYzAAFQFbANltPUTEKAALVDhkRDBSTIBRVHTURgByGE9MABtSbzAoRG9ESrpisR09AF8+BmItdq0tCAQ6OrhMCzB0CqkrLAdGdg4Afl5h1BgwDgkZRA1EdtaAegPEgD1F-sGwYf1SAEcQGAMaabRZ3EZ5zhWoNY2t+L2h2OejOFyGdQqcDgAGsALLoABycAAgs4XtY5v8doCtEdTucBuD6iAIClUVx0W8PsBHsNvr8OAAaRB0UiXGi8XBQqr8LG7fa44G6M5AA

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bentenOP•3y ago

thanks homie Hmm, so this works with the spread args but not for explicitly declaring args. For example,

export function createLoader<LDR extends (ctx: Context, input: Record<string, string[]>) => any>(loader: LDR) {
    function loaderSetup(input: Parameters<LDR>[1]) {
      //...
    }
    return loaderSetup;
}

export function createLoader<LDR extends (ctx: Context, input: Record<string, string[]>) => any>(loader: LDR) {
    function loaderSetup(input: Parameters<LDR>[1]) {
      //...
    }
    return loaderSetup;
}

CaptainStarz•3y ago

https://www.typescriptlang.org/play?#code/JYOwLgpgTgZghgYwgAgMIHtwQB5mQb2QF8AoEsATwAcUAVOYAGwB5aA+ZAXmVuR0hAATAM7IA2gFcQAaxDoA7iAA0yAHTqAFKBjQeDRgEoAusgD8epsgBcyEBABu0MjirooeGFIRhgmZAigIOEgAGXQ4QWhmEmRY5ABJECoJPH4IIVEAJQgEN0FmYTAoUABzFULikBKxIzYlGLiQgBFMvlx0kWQNXKxcGwxesBVQZLAbRNGDLg44EAoSNg1GcMioG2bMqfwG2M8Qb18QZGWI6ABlCDAJKg11VTgoEuEbeiZmAAUHuABbS+hhZgbNhsLY7OKxAD0ELuYNI4MCVygRxOqwuVyoAG4SKQSD1CsgYFx-IFghAwqcoBpumBsMMkikbIQ4DYKqUasQppwOIQiAYSFDwQA9UxkPF4EpEgJBUIraBU7zYTncjn8iFCkVAA so much types 😕

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bentenOP•2y ago

Hey just wanted to say I finally got around to using this and it worked great. So thank you ❤️ @CaptainStarz

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Help me type this function