Follow-up to #54002 that:
* Remove the `toString` implementation from the `primitives`.
* Guards the `toString` with `ngDevMode` and prints out the value.
PR Close#54079
Since signals are function, currently stringifying them reveals the implementation of the function. This can lead to confusion since it contains internal implementation details. These changes add static `toString` function to address the issue.
**Note:** it's tempting to have `toString` output the actual value of the signal, but that would encourage users not to call the function which will be problematic in the long run. That's why these changes are using a static string instead.
PR Close#54002
For the implementation of input signals, we want to extend the signal
primitive. The basic methods exposed here are not suitable as we'd like
to store additional metadata on the reactive node, and also have a
custom getter (for required inputs and throwing).
To enable this, one small piece was missing. This commit exposes it and
also improves type safety, now that `SignalNode` is typed properly after
the previous commit.
PR Close#53571
The `SignalNode` interface, describing the reactive node for a `Signal`,
seemingly exposes the `SIGNAL` symbol as a class member. This is not
true as the `SIGNAL` reactive node only exists on the getter function,
as a way to retrieve the signal underlying reactive node.
This commit fixes this, enabling improved type-safety later, in a
follow-up commit where `SIGNAL_NODE` can now be typed to match the
`SignalNode` interface (unlike now where it's typed as just `object`).
PR Close#53571
The PR https://github.com/angular/angular/pull/52465 introduced short-circuit for
the signal equality invocation - with the reasoning that the equality function
should never return false for arguments with the same references. In practice it
turned out that it is rather surprising and the subsequent PR
https://github.com/angular/angular/pull/52532 added a warning when the short-circuit
was taking priority over the equality function.
Still, the presence of the short-circuit prevents people from mutating objects in
place and based on https://github.com/angular/angular/issues/52735 this is a common
and desired scenario. This change removes the short-circuit altogether and thus
fixes the mentioned issue.
We do recognize that removing short-circuit exposes developers to the potentially
surprising logic where mutated in-place change won't be propagated throug the
reactivity graph (due to the deault equality function). But we assume that this might
be less surprising / more desirable as compared to the short-circuit logic.
Fixes#52735
PR Close#53446
This change skips signal equality calls on set / update when the
two values (current and the new one) are referentially identical.
The assumption is that equality function implementation should
never return false for 2 values that are the same (according to
the Object.is logic).
PR Close#52465
This commit adds a global epoch to the reactive graph, which can optimize
non-live reads.
When a non-live read occurs, a computed must poll its dependencies to check
if they've changed, and this operation is transitive and not cacheable.
Since non-live computeds don't receive dirty notifications, they're forced
to assume potential dirtiness on each and every read.
Using a global epoch, we can add an important optimization: if *no* signals
have been set globally since the last time it polled its dependencies, then
we *can* assume a clean state. This significantly improves performance of
large unwatched graphs when repeatedly reading values.
PR Close#52420
This change removes the `mutate` method from the `WritableSignal` interface and
completely drops it from the public API surface.
The initial API proposal for Angular signals included the mutate method, allowing
in-place modification of JS objects, without changing their references (identity).
This was based on the reasoning that identity change on modification is not necessary
as we can send the “modified” notification through the signals graph.
Unfortunately the signal-specific change notification is lost as soon as we read
signal value outside of a reactive context (outside of a reactive graph).
In other words - any code outside of the Angular signals library can’t know
that an object is modified.
Secondly, to make the mutate method work, we’ve defaulted the signal value equality function
to the one that considers non-primitive values as always different.
This is unfortunate for people working with immutable data structures
(this is notably the case for the popular state management libraries)
as the default equality function de-optimizes memoization in computed,
making the application less performant.
Given the above reasons we prefer to remove the mutate method in the signals library -
at least for now. There are just too many sharp edges and tradeoffs that we don’t fully
understand yet.
BREAKING CHANGE:
The `mutate` method was removed from the `WritableSignal` interface and completely
dropped from the public API surface. As an alternative please use the update method and
make immutable changes to the object.
Example before:
```typescript
items.mutate(itemsArray => itemsArray.push(newItem));
```
Example after:
```typescript
items.update(itemsArray => [itemsArray, …newItem]);
```
PR Close#51986
This commit reorganizes the Angular code a bit, and moves signals into a
newly defined `@angular/core/primitives` location. This will be used inside
g3 to allow non-Angular targets to depend on the signals core without
incurring a dependency on the whole framework.
PR Close#51986
Kristiyan Kostadinov