Non-Inferred Generics

generic-inference2.ts

// the example from typescript's docs
function getProperty<T, K extends keyof T>(obj: T, key: K) {
    return obj[key];
}

interface FourLetters {
  a: number
  b: number
  c: number
  d: number
}

let x = { a: 1, b: 2, c: 3, d: 4 }

// calling generic explicitly (the first way I thought generics could be called)
getProperty<FourLetters, keyof FourLetters>(x, "a"); // okay

// providing a default value in the definition
function getProperty_withDefaults<T extends {} = {}, K extends keyof T = keyof T>(obj: T, key: K) {
    return obj[key];
}

// calling a generic with inference even though it has a default
getProperty_withDefaults({ a: 1 }, 'a')