31 lines
847 B
TypeScript
31 lines
847 B
TypeScript
/**
|
|
* Fetchable addresses the reality that most of our resources exist in three
|
|
* distinct possible states.
|
|
* - not loaded: it may or may not exist, but I don't have a copy of it
|
|
* - not found: I've asked and know definitively that this does not exist
|
|
* - value present
|
|
*/
|
|
export type Fetchable<T> = 'loading' | 'not loaded' | 'not found' | T;
|
|
|
|
export function hasValue<T>(f: Fetchable<T>): f is T {
|
|
return f !== 'not found' && f !== 'not loaded' && f !== 'loading';
|
|
}
|
|
|
|
export function valueOf<T>(f: Fetchable<T>): T | null {
|
|
return !hasValue(f) ? null : f;
|
|
}
|
|
|
|
export function withValue<T, V>(f: Fetchable<T>, fun: (val: T) => V): V | null {
|
|
return !hasValue(f) ? null : fun(f);
|
|
}
|
|
|
|
export function use<T, V>(f: Fetchable<T>, fun: (val: T) => V): Fetchable<V> {
|
|
if (!hasValue(f)) {
|
|
return f;
|
|
} else {
|
|
return fun(f);
|
|
}
|
|
}
|
|
|
|
|