Generics

• A type parameter that we pass to another type
• Types that behave the same way, regardless of the type
• Using the type parameter makes sure that we always work with the same type (as input, output, modifications, ...)

Problem

• Let's say we have a class Queue (first in, first out):

class Queue {
  private data = [];
  push(item) { this.data.push(item); }
  pop() { return this.data.shift(); }
}

• In this case we can add anything (string, number, object, ...) to the queue and when we pop it, it can be anything
• This might be a problem if we need to perform some business logic inside our Queue, like for example calculations (this won't work on non-numeric types)

Solution

• We can add a type parameter to the class, so when we use the class we already provide which type we are working with

class Queue<T> {
    private data = [];
    push(item: T) { this.data.push(item); }
    pop(): T | undefined { return this.data.shift(); }
  }
  
  const queue = new Queue<number>();
  queue.push(0);
  queue.push("1"); // ERROR : cannot push a string. Only numbers allowed