@psalm-immutable is not the same as adding @psalm-readonly/@psalm-mutation-free

[kkmuffme]

Used to annotate a class where every property is treated by consumers as @psalm-readonly and every instance method is treated as @psalm-mutation-free

But it seems this isn't true: https://psalm.dev/r/2d7cd6c403 When using with immutable, the errors are different: https://psalm.dev/r/c68a1c73d6

You could argue: the class might be extended and then that wouldn't be true anymore - however this is irrelevant for what is in the class for now, and has to be adjusted in the extending class. However, adding final to disallow extending, still gives the same errors: https://psalm.dev/r/67c22e0ca6

[psalm-github-bot[bot]]

I found these snippets:

https://psalm.dev/r/2d7cd6c403

```php bar = $arg; } /** * @psalm-mutation-free * @psalm-pure * @return string */ public function get_bar() { return $this->bar; } } ``` ``` Psalm output (using commit 2c50745): ERROR: ImpureVariable - 20:14 - Cannot reference $this in a pure context ERROR: ImpurePropertyFetch - 20:14 - Cannot access a property on a mutable object from a pure context ```

https://psalm.dev/r/34441531c4

```php bar = $arg; } /** * @psalm-pure * @return string */ public function get_bar() { return $this->bar; } } ``` ``` Psalm output (using commit 2c50745): ERROR: ImpureVariable - 19:14 - Cannot reference $this in a pure context ERROR: ImpurePropertyFetch - 19:14 - Cannot access a property on a mutable object from a pure context ```

https://psalm.dev/r/67c22e0ca6

```php bar = $arg; } /** * @psalm-mutation-free * @psalm-pure * @return string */ public function get_bar() { return $this->bar; } } ``` ``` Psalm output (using commit 2c50745): ERROR: ImpureVariable - 20:14 - Cannot reference $this in a pure context ERROR: ImpurePropertyFetch - 20:14 - Cannot access a property on a mutable object from a pure context ```

[orklah]

Your two first link shows exactly the same errors

[kkmuffme]

Sorry, copied the wrong one, fixed now.

[ygottschalk]

@readonly @mutation-free: https://psalm.dev/r/232ed66d3b @immutable: https://psalm.dev/r/5c9610e802

Both show the same (aka no) errors.

You had a @pure on the method which caused the errors...

[psalm-github-bot[bot]]

I found these snippets:

https://psalm.dev/r/232ed66d3b

```php bar = $arg; } /** * @psalm-mutation-free * @return string */ public function get_bar() { return $this->bar; } } ``` ``` Psalm output (using commit 2c50745): No issues! ```

https://psalm.dev/r/5c9610e802

```php bar = $arg; } /** * @return string */ public function get_bar() { return $this->bar; } } ``` ``` Psalm output (using commit 2c50745): No issues! ```

[kkmuffme]

I know that the @pure caused the errors, but why are the errors different depending on whether I use immutable on the class or readonly/mutation-free on all properties?

[ygottschalk]

bcs you can actually 'use' an immutable object in a pure context.

Since the @immutable annotation gives psalm the guarantee that really all properties are readonly and all methods do not mutate, the ImpurePropertyFetch issue will be gone.

Used to annotate a class where every property is treated by consumers as @psalm-readonly and every instance method is treated as @psalm-mutation-free

The docs never claim, that it is the same to use either @immutable or @readonly @mutation-free, but state that using @immutable will make every property be treated like having the @readonly and every method like having @mutation-free. BUT: Using @immutable gives knowlege about the 'bigger picture', therefore psalm does know more about the class itself.

[ygottschalk]

Another difference is, if you use @immutable, all child classes need to be marked as @immutable, too.