548290b006
* Run a minor code quality checker over the repo Largely targeted at spelling of common words and misc code issues. * Update snapshots
59 lines
1.6 KiB
TypeScript
59 lines
1.6 KiB
TypeScript
/*
|
|
Copyright 2021 The Matrix.org Foundation C.I.C.
|
|
|
|
Licensed under the Apache License, Version 2.0 (the "License");
|
|
you may not use this file except in compliance with the License.
|
|
You may obtain a copy of the License at
|
|
|
|
http://www.apache.org/licenses/LICENSE-2.0
|
|
|
|
Unless required by applicable law or agreed to in writing, software
|
|
distributed under the License is distributed on an "AS IS" BASIS,
|
|
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
|
|
See the License for the specific language governing permissions and
|
|
limitations under the License.
|
|
*/
|
|
|
|
/**
|
|
* Utility class for lazily getting a variable.
|
|
*/
|
|
export class LazyValue<T> {
|
|
private val: T;
|
|
private prom: Promise<T>;
|
|
private done = false;
|
|
|
|
public constructor(private getFn: () => Promise<T>) {
|
|
}
|
|
|
|
/**
|
|
* Whether or not a cached value is present.
|
|
*/
|
|
public get present(): boolean {
|
|
// we use a tracking variable just in case the final value is falsy
|
|
return this.done;
|
|
}
|
|
|
|
/**
|
|
* Gets the value without invoking a get. May be undefined until the
|
|
* value is fetched properly.
|
|
*/
|
|
public get cachedValue(): T {
|
|
return this.val;
|
|
}
|
|
|
|
/**
|
|
* Gets a promise which resolves to the value, eventually.
|
|
*/
|
|
public get value(): Promise<T> {
|
|
if (this.prom) return this.prom;
|
|
this.prom = this.getFn();
|
|
|
|
// Fork the promise chain to avoid accidentally making it return undefined always.
|
|
this.prom.then(v => {
|
|
this.val = v;
|
|
this.done = true;
|
|
});
|
|
|
|
return this.prom;
|
|
}
|
|
}
|