Can you please explain the significance of classes <T> and <U> in Angular 2?

After diving into the Angular 2 TypeScript documentation, I have come across these two classes frequently. Can someone provide a detailed explanation of what they are?

One example code snippet from the QueryList API documentation showcases:

class QueryList {
    changes : Observable<any>
    length : number
    first : T
    last : T
    map(fn: (item: T, index: number, array: T[]) => U) : U[]
    filter(fn: (item: T, index: number, array: T[]) => boolean) : T[]
    reduce(fn: (prevValue: U, curValue: T, curIndex: number, array: T[]) =>      U, init: U) : U
    forEach(fn: (item: T, index: number, array: T[]) => void) : void
    some(fn: (value: T, index: number, array: T[]) => boolean) : boolean
    toArray() : T[]
    toString() : string
    reset(res: Array<T|any[]>) : void
    notifyOnChanges() : void
    setDirty()
    dirty 
}

Answer №1

Those are called Generics, which have the ability to represent any type:

TypeScript - A Guide to Generics

This feature allows for the creation of functions that can work with various types while still maintaining consistency within the function (the specified T must be consistently used as T throughout the entire function).

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