Anders give this example of an interface overload, but I don't get how it would be implemented and used:
interface Fooable
{
Foo(n:number) : string;
Foo(s:string) : string;
}
Can someone give me an example of implementing and using this?
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Possible duplicate of Functions Overloading in interface and classes - how to?Louis– Louis2017-03-06 21:08:01 +00:00Commented Mar 6, 2017 at 21:08
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1 Answer
class Bar implements Fooable {
Foo(n: number): string;
Foo(n: string): string;
Foo(n: any) {
if(typeof n === 'number') {
return n + ' is a number';
} else if(typeof n === 'string') {
return n + ' is a string';
} else {
throw new Error("Oops, null/undefined?");
}
}
}
7 Comments
Greg Gum
Thanks very much. In testing this, it seems
Foo(n: number): string; isn't actually required in the class (it compiles without error without it.) What is the purpose of that line?
Ryan Cavanaugh
What do you mean? I get an error removing either overload.
Greg Gum
See below for example.
Ryan Cavanaugh
Removing two lines is different than removing one line! You can satisfy the interface by providing a function that is a subtype of the required function. In other words, a function that can take anything and returns a string is an acceptable substitute for a function that can take a number or a string and return a string.
Ryan Cavanaugh
They indicate what you can call the function with. For example, you can't call bar.Foo({n: 3});
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