Improve mapValue: log errors, permit Computed<U> returns
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@ -47,7 +47,7 @@ export class Property<T> implements Computed<T> {
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}
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// mapValue attaches a callback for the resolution of a computed value, and returns a newly computed value.
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public mapValue<U>(callback: (v: T) => U): Computed<U> {
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public mapValue<U>(callback: (v: T) => U | Computed<U>): Computed<U> {
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let result = new Property<U>();
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this.outputPromise.then((value: T | undefined) => {
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// If the value is unknown, propagate an unknown. Otherwise, use the callback to compute something new.
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@ -55,7 +55,23 @@ export class Property<T> implements Computed<T> {
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result.setOutput(undefined, true, false);
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}
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else {
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result.setOutput(callback(value), true, false);
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try {
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// There's a callback; invoke it.
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let u: U | Computed<U> = callback(value);
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// If this is another computed, we need to wire up to its resolution; else just store the value.
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if ((u as Computed<U>).mapValue) {
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(u as Computed<U>).mapValue((v: U) => {
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result.setOutput(v, true, false);
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});
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}
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else {
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result.setOutput(<U>u, true, false);
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}
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}
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catch (err) {
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Log.error(`MapValue of a Computed yielded an unhandled error: ${err}`);
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}
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}
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});
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return result;
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