Could someone please assist me in understanding why we use angular brackets <> in typescript? For example, I have provided some code below and would appreciate an explanation.
export class HomePage {
constructor(public navCtrl: NavController) {
let a = this.testfunc<boolean>(4);
console.log(a);
}
testfunc<T>(s) {
return s;
}
}
Thank you
These are signs of generics. When you see
testfunc<T>(s){ return s; }testfunc can accept a generic type parameter T. Using testfunc<boolean>(4) is providing a specific type argument (boolean) for that type parameter. In the given example, it may not have much impact since testfunc isn't utilizing T, but consider this:
function foo(arg: string) {
let numbers: Array<number> = [];
numbers[0] = arg; // Error: Type 'string' is not assignable to type 'number'.
}
In this case, numbers is defined as an array of number, which leads to an error when trying to assign a string value like arg.
Now, take a look at this alternative scenario:
function foo<T>(arg: T) {
let numbers: Array<T> = [];
numbers[0] = arg; // Error
}
Here, foo doesn't need to know the content of numbers, just that it will match the type of arg. This allows for valid calls like:
foo<number>(4);
foo<string>("bar");
While I've shown explicit type arguments in these calls, TypeScript can often infer them automatically:
foo(4);
foo("bar");
Generics, enclosed in angled brackets, are a powerful feature in programming that allow you to create placeholders for types within a class. This flexibility enables you to specify the type of fields and methods at a later time.
export class HomePage {
constructor(public navCtrl: NavController) {
let a = this.testfunc<boolean>(4);
console.log(a);
}
testfunc<T>(s){
return s;
}
}
In the testFunc method, the T inside the angle brackets serves as a type argument, indicating that the method can work with any data type.
The use of generics provides a level of freedom not found in other approaches. For instance, by employing a generic method, it becomes possible to pass in any type as its type argument.
function Rand(value: T) { ... }
If T is set as a string, all occurrences of T within that function must adhere to the string type, as is the case for other data types as well.
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