function identity<String>(arg: String): String {
return arg;
}
let myIdentity = identity([2]);
console.log()
Hi could someone help me to understand why this doesn't throw any type error even if i am passing a array of numbers ?
function identity<string>(arg: string): string {
return arg;
}
let myIdentity = identity([2]);
console.log(myIdentity )
'string' is declared but its value is never read.
You are shadowing the builtin types String and string by using their names as your generic parameter. Just use a parameter name that is not a built-in to solve it:
function identity<T extends string>(value: T): T {
return value;
}
identity([2]); // error [2] doesn't extend string
identity('2'); // ok
If you want a generic identity function without any kind of constraint, you can use an unconstrained type parameter:
function identity<T>(value: T): T {
return value;
}
const numberArrayValue = identity([2]); // number[]
const objectValue = identity({b: 2}); // { b: number; }
const stringLiteralValue = identity('2'); // "2"
const numberLiteralValue = identity(2); // 2