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
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
This commit refactors the signals API surface of Angular out of the
//packages/core/src/signals package. This is done in preparation of moving
the core signals package into a new 'primitives' package that's decoupled
from the public API.
PR Close#51986
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#51821
This PR moves the Observable subscription of toSignal outside of the
reactive context. As the result the toSignal calls are allowed in the
computed, effect and all other reactive consumers.
This is based on the reasoning that we already allow signals creation
in a reactive context. Plus a similar change was done to the async pipe
in the https://github.com/angular/angular/pull/50522Fixes#51027
PR Close#51831
This commit moves the destroy logic from 'effect' in the lower-level
'watch' so this implementation is shared among varius watch implementations.
PR Close#51757
When a producer is no longer used, the consumer has to update its internal data structure
that keeps track of all producers. There used to be an issue where only half of the stale
producers would actually be removed from this data structure, as the intended upper bound
of the number of producers to remove would decrease with each removed producer, therefore
not reaching all producers that should be removed from the data structure.
This commit fixes the issue by truncating the arrays directly, without going through
individual `pop` operations. An assertion that would catch the inconsistent state in
the internal data structures of the signal graph has been introduced.
PR Close#51722
This commit switches the signals library from a bidirectional symmetric
dependency graph using weak references, to a bidirectional _asymmetric_
graph which uses strong references. This is made possible with a reference
counting algorithm which only tracks producer -> consumer references for
effect-like "live" consumers, preventing memory leaks.
The new algorithm should be simpler and faster than the previous
implementation as weak references are fairly slow to create and traverse.
A tradeoff is that non-live consumers must now poll their producers when
read, as they cannot rely on dirty notifications.
As part of this refactoring, the `ReactiveNode` class is replaced with an
interface instead, and methods are moved to standalone functions. This is
paired with instantiating individual signals/computeds via `Object.create`
against a prototype node which contains static or initial values. This
technique, in conjunction with the rest, greatly improves the performance
of node creation.
PR Close#51226
Unlike the current signature where the input argument must a function, this change allows an input of any type to be passed to the `isSignal` function.
PR Close#50035
The new asReadonly method on the WritableSignal interface makes
it possible to create readonly instance of a writable signal.
Readonly signals can be accessed to read their value,
but can't be changed using set, update or mutate methods.
PR Close#49802
This change makes is possible to use async functions
(ones returning a promise) as effect run functions.
To make it possible, the signature of the effect function
changed: effect cleanup function is registered now
(using a dedicated callback passed to the effect creation)
instead of being returned from the effect function.
PR Close#49783
This commit adds a hook to `WritableSignal` that is called whenever the
signal's value is updated via the mutation API. This hook allows consumers
to implement logic which is synchronous with signal sets (e.g. executing
effects). It's currently unused.
PR Close#49708
* Prevent reads of signals during the notification process. This shouldn't
ever be triggered by user code but is more of a preventative for
internal misuse. Reading a signal during notification would/could create
glitches where the values being read are not updated to reflect the
values being updated by the notification.
* Prevent signal writes inside of computed's. These are meant to be
derived values and should not have any side-effects like writing new
values to other signals
* Prevent signal writes inside of effects by default. Writing to signal
values during the execution of an effect can lead to the
`ExpressionChangedAfterItHasBeenCheckedError` if writing to signals
that represent global state which is read in a parent component. This is
mostly just a problem for `OnPush`/`CheckAlways` components, but with
signals being new and pure signal components not even available yet,
it will be the majority for a long time.
PR Close#49631
We've been experimenting with the DeepReadonly type that would make
signal values deeply read-only and prevent accidental changes without
going to the owner of data. What we've found out during the experiments
is that additional safety net has more drawbacks than benefits: it just
introduces too much friction to be practical for daily usage.
PR Close#49154
This change extends the effect API surface so effects can, optionally,
return a cleanup function. Such function, if returned, is executed
prior to the subsequent effect run.
PR Close#49625
This commit adds a `DeepReadonly` type to the signals API, and makes signal
getters return an immutable version of their value type. This doesn't
prevent all mutation but adds some friction against modifying the values
within signals outside of the proper mutation APIs.
PR Close#49529
The `effect` implemented in the signal library is useful for testing but
does not integrate with Angular. This commit moves that code to the
actual framework package and integrates it with automatic cleanup via
`DestroyRef`. A simpler effect implementation is used in the signal tests to
test the `Watch` primitive.
Further commits will update the scheduling to tie effects together with
change detection.
PR Close#49529
This commit switches the `signal` and `computed` APIs to accept an optional
options argument as their second argument, instead of an equality function
directly. The equality function has moved to an option in the options
argument.
PR Close#49529
This commit exposes `signal`, `computed`, `effect` and various helpers from
the `@angular/core` entrypoint.
These APIs are marked as `@developerPreview` and are still prototypes in
active development. Their final shapes will be subject to our internal
design reviews as well as one or more community RFCs. We're exporting them
now to allow for experimentation using 16.0.0 next and RC releases.
PR Close#49150
This commit checks in (but does not export) a prototype implementation of
Angular Signals, along with its unit test suite and a README explaining the
algorithms used.
Signals are not a new concept in the framework space, but there are many
different flavors of implementations. These differ radically both in terms
of public API as well as behavioral details (such as eager vs lazy
computation, batching behavior, equality, cleanup, nesting, etc).
This commit comprises a bespoke implementation that we've designed to best
meet Angular's needs, especially when it comes to compatibility and
flexibility of use within existing applications.
Many of the API features of this implementation of signals, as well as the
larger direction of reactivity in Angular, will be discussed in future RFCs.
Co-Authored-By: Pawel Kozlowski <pkozlowski.opensource@gmail.com>
PR Close#49091
