Here is a code snippet for you to consider:
//LINE 1
private result: Map<EventType<any>, number> = new HashMap<EventType<any>, number>();
//LINE 2
private result: Map<EventType<any>, number> = new HashMap();
When the variable type is an interface, do you need to include generics in the implementation constructor? Are there any differences in TypeScript between the two lines of code?
There is no discernible difference between the two lines in terms of their runtime behavior. Types are completely erased at compile time, so it should not have any impact on runtime performance.
Will the type parameters resolve to the same values? TypeScript will perform type inference based on the expected return value. For example, if it expects the constructor's result to be
Map<EventType<any>, number>HashMap constructor should be EventType<any> and number.
This can be observed by hovering over the HashMap constructor:
export class Map<K, V> {
get(k: K): V { return null!; }
}
export class HashMap<K, V> extends Map<K, V> {
get(k: K): V { return null!; }
}
let o: Map<string, number> = new HashMap() // hover over HashMap and you will see constructor HashMap<string, number>(): HashMap<string, number>
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