fr(cdk/coercion): coercion decorators

Feature Description

Instead of repetitive

@Input()
set disabled(disabled: boolean) {
  this._disabled = coerceBooleanProperty(disabled);
}
get disabled() {
  return this._disabled;
}
private _disabled = false;

We could write:

@Input()
@CoerceBoolean()
disabled = false;

Use Case

Describe the use case(s) that the proposed feature would enable.

I think the coercion methods the CDK provides are super useful as they are for anyone writing serious libraries. I do however find myself writing the same setters and getters over and over again, and in conjunction with strictTemplates and ngAcceptInputType_* this get’s a bit cumbersome.

So I am wondering now if maybe we could get some decorators in place instead? Are there any serious downsides to it that I fail to see at the moment?

A first POC CoerceBoolean decorator:

function CoerceBoolean() {
  return function(target: object, propertyKey: string, descriptor?: PropertyDescriptor) {
    let _value = false;

    return Object.defineProperty(target, propertyKey, {
      set(value: BooleanInput) {
        _value = coerceBooleanProperty(value);
        descriptor?.set?.(_value);
      },
      get() {
        return descriptor?.get?.() ?? _value;
      },
      configurable: descriptor?.configurable,
      enumerable: descriptor?.enumerable,
    });
  };
}

[devversion]

Correct. View Engine does not strip decorators away at all. Ivy only strips Angular-known decorators away. Angular build-optimizer only strips known Angular decorators either.

So that definitely could work. If I recall correctly though, there were implications in terms of tree-shaking. I think we can track this as an upstream issue as the components team believes in this being something that should be addressed at framework level.

• https://github.com/angular/angular/issues/8968.
• https://github.com/angular/angular/issues/14761

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