Angular signal computed(() => toSignal()) throws Error

Question

Following code

  source$ = of(1);
  value = computed(() => toSignal(this.source$));

  constructor() {
    effect(() => {
      console.log(this.value());
    });
  }

Throws ERROR Error: NG0602: toSignal() cannot be called from within a reactive context. Invoking toSignal causes new subscriptions every time. Consider moving toSignal outside of the reactive context and read the signal value where needed. Find more at https://angular.io/errors/NG0602

Why do I get this error? I know that I could just use the toSignal without computed then it works. However I want to make use of the computed-memoization.

When splitting it up in two steps it does not throw:

  source$ = of(1);
  v =  toSignal(this.source$);

  value = computed(() => this.v());

  constructor() {
    effect(() => {
      console.log(this.value());
    });
  }

Answer 1

computed() is not supposed to create new signals (inside the computation function), it should derive (in other words, "compute") the new value from values of one or multiple signals.

I know that I could just use the toSignal without computed then it works. However I want to make use of the computed-memoization.

Regular signals also use memoization - they will not notify consumers if the new value is equal to the existing one (source code).