Created
April 14, 2016 14:01
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(TypeScript) typeswitcher, like switch, but with constructor based cases and expressions with inferred types
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/** | |
* Usage: | |
typeSwitch(someInstance, defaultvalue) | |
.when(MyClass, i => result) | |
.when(OtherClass, i => otherResult) | |
.get() | |
In the expressions, the type of the 'i' param should be inferred correctly, see the attribute default value checks | |
*/ | |
export function typeSwitch<T, R>(instance: T, defaultValue?: R): TypeSwitcher<T, R> { | |
return new TypeSwitcher<T, R>(instance, defaultValue); | |
} | |
interface ITypeSwitchEntry<T, R> { | |
type: new (...args: any[]) => T; | |
expr: (instance: T) => R; | |
} | |
interface IConstructor<T> { | |
new (...args): T; | |
} | |
class TypeSwitcher<T, R> { | |
private cases: ITypeSwitchEntry<T, R>[] = []; | |
constructor(private instance: T, private _defaultValue?: R) { } | |
when<Z extends T>(clazz: IConstructor<Z>, expr: (instance: Z) => R): TypeSwitcher<T, R> { | |
this.cases.push({ type: clazz, expr: expr }); | |
return this; | |
} | |
get(): R { | |
for (var i = 0, l = this.cases.length; i < l; i++) | |
if (this.instance instanceof this.cases[i].type) | |
return this.cases[i].expr(this.instance); | |
if (this._defaultValue !== undefined) | |
return this._defaultValue; | |
throw new Error("Unsupported type: " + this.instance); | |
} | |
} |
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