Make generic Interface in typescript

Question

The Generic part in below line in abc which is in <> .

Actually as I am coming from Javascript side to Typescript side in angular 2 .

That's why I am not seen these Generic part in Javascript .

export interface Animals<abc>

export class WaterAnimal <abc> implements Animals<abc> { }

Things which I get :

Generic Part helps to maintain the type which we are sending and achieving from any function will be of same type that type can be any Object,String,Number or Array.

Eg :-

function identity<T>(arg: T): T {
    return arg;
}

Things I want to Ask:-

When We come in Classes and Interfaces :- by passing the parameters in Interface as in Animals interface what is the purpose of it .
If there is any purpose which i don't aware of yet ,now if we implements that Animal Interface to WaterAnimal Class then I want to write <abc> infront of Animal Interface because while defining that Interface I have pass that thing as parameter into it .So Why complier is forcing me to define <abc> with the WaterAnimal Class ..Is there is any Reason behind this..

Any help will be appreciated .

maybe you should read more about generic programming in general. en.wikipedia.org/wiki/Generic_programming — toskv
– toskv, Commented Jun 7, 2017 at 9:49

Fenton · Accepted Answer · 2017-06-07 10:55:22Z

3

A good example of Generics exists in the language itself.

Most languages had forms on un-typed lists, like the JavaScript Array:

var arr = [
    1,
    "str",
    new Customer()
];

But a much more useful object is an array that only contains a single type - because then you can iterate the array knowing everything is the same:

var arr: NumberArray = [
    1,
    3,
    5
];

But we would need to create a new type for each kind of array, so we would end up with NumberArray, StringArray, CustomerArray... and so on.

So instead of creating a nearly infinite number of types, we create a generic one. We then specify what type we intend to use:

var arr: Array<number>= [
    1,
    3,
    5
];

The type argument (number) allows us to re-use the Array class or interface rather than create new kinds. The condition on this is that Array cannot know anything about this type unless we specify a type constraint.

To understand how this can be used within a generic class, here is a quick fake example:

class ArrayOfOne<T> {
    private item: T;

    add(item: T) {
        this.item = item;
    }

    retrieve() : T {
        return this.item;
    }
}

In this example, the ArrayOfOne class doesn't need to know what T is, but if you use it, T will be strongly typed.

var arr = new ArrayOfOne<string>();
arr.add("str"); // ok
arr.add(1); //not ok

var str: string = arr.retrieve(); // ok
var num: number = arr.retrieve(); // not ok

answered Jun 7, 2017 at 10:55

Fenton

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1 Comment

hardy Over a year ago

Nice Explain . But I dont knw why my editor is forcing me to put <string> when I make export interface Animals<abc> export class WaterAnimal <abc> implements Animals<abc> { } Basically I am asking for second point in Question above...

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