Consider this straightforward property access function
export function accessProperty<T, K extends keyof T, P extends T[K]>(name: K, v: T): P {
return v[name] as P
}
What is the significance of the cast as P in this context?
I experimented with different approaches
export function accessProperty<T, K extends keyof T, P = T[K]>(name: K, v: T): P
export function accessProperty<T, K extends keyof T, P extends T[K] = T[K]>(name: K, v: T): P
yet the cast remains necessary in all cases
The definition of generics states that every instance of P is a type of T[K], however, it does not necessarily mean that every T[K] is an instance of P. To address this issue, you can directly use the type T[K].
For example:
export function accessProperty<T, K extends keyof T>(name: K, value: T): T[K] {
return value[name];
}
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