42 lines
1.7 KiB
TypeScript
42 lines
1.7 KiB
TypeScript
// Copyright 2016-2018, Pulumi Corporation.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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/**
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* Common code for doing RTTI typechecks. RTTI is done by having a boolean property on an object
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* with a special name (like "__resource" or "__asset"). This function checks that the object
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* exists, has a **boolean** property with that name, and that that boolean property has the value
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* of 'true'. Checking that property is 'boolean' helps ensure that this test works even on proxies
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* that synthesize properties dynamically (like Output). Checking that the property has the 'true'
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* value isn't strictly necessary, but works to make sure that the impls are following a common
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* pattern.
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*/
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/** @internal */
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export function isInstance<T>(obj: any, name: keyof T): obj is T {
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return hasTrueBooleanMember(obj, name);
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}
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/** @internal */
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export function hasTrueBooleanMember(obj: any, memberName: string | number | symbol): boolean {
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if (obj === undefined || obj === null) {
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return false;
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}
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const val = obj[memberName];
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if (typeof val !== "boolean") {
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return false;
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}
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return val === true;
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}
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