What is a generic?

Learn functions with type parameters.

What is a generic?

A generic lets a function or class take a type as a parameter. The letter inside angle brackets <T> is a type parameter that is replaced by the real type when called. The same function then works type-safely with different types.

function ilk<T>(dizi: T[]): T {
  return dizi[0];
}
const s = ilk<number>([1, 2, 3]);
const m = ilk<string>(["a", "b"]);

Without generics

Without generics you would write a separate function per type: ilkSayi, ilkMetin, etc. With a single ilk<T> the same function works for all types and the compiler still catches wrong usage. This keeps type safety while reducing duplication.

Exercise Return the last element

Write a generic function son<T> with parameter dizi: T[] and return type T. It should return the last element of the array. Then print the result of son([10, 20, 30]) with console.log.

Show example solution

function son<T>(dizi: T[]): T {
  return dizi[dizi.length - 1];
}
console.log(son([10, 20, 30]));

Test yourself

What does T represent in the function below?
```
function ilk<T>(dizi: T[]): T
```
- Type parameter
- Fixed number type
- A variable name
- An interface name
Show answer

Type parameter — T is a type parameter; it is replaced by a real type such as number or string when called. It is not a variable name or an interface name.

Add the type parameter

function kimlik<____>(x: T): T {
  return x;
}

Show answer

function kimlik<T>(x: T): T {
  return x;
}

Generic parts

<T>

Type parameter declaration
ilk<number>(...)

Calling with a type argument
T[]

Type parameter used as array
function ilk

Generic function name

Next lesson: Generic functions

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