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111 lines
2.4 KiB
Markdown
111 lines
2.4 KiB
Markdown
# Adding assertions
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Psalm has three docblock annotations that allow you to specify that a function verifies facts about variables and properties:
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- `@psalm-assert` (used when throwing an exception)
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- `@psalm-assert-if-true`/`@psalm-assert-if-false` (used when returning a `bool`)
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A list of acceptable assertions [can be found here](assertion_syntax.md).
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## Examples
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If you have a class that verified its input is an array of strings, you can make that clear to Psalm:
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```php
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<?php
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/** @psalm-assert string[] $arr */
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function validateStringArray(array $arr) : void {
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foreach ($arr as $s) {
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if (!is_string($s)) {
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throw new UnexpectedValueException('Invalid value ' . gettype($s));
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}
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}
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}
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```
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This enables you to call the `validateStringArray` function on some data and have Psalm understand that the given data *must* be an array of strings:
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```php
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<?php
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function takesString(string $s) : void {}
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function takesInt(int $s) : void {}
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function takesArray(array $arr) : void {
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takesInt($arr[0]); // this is fine
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validateStringArray($arr);
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takesInt($arr[0]); // this is an error
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foreach ($arr as $a) {
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takesString($a); // this is fine
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}
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}
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```
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Similarly, `@psalm-assert-if-true` and `@psalm-assert-if-false` will filter input if the function/method returns `true` and `false` respectively:
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```php
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<?php
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class A {
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public function isValid() : bool {
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return (bool) rand(0, 1);
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}
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}
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class B extends A {
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public function bar() : void {}
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}
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/**
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* @psalm-assert-if-true B $a
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*/
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function isValidB(A $a) : bool {
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return $a instanceof B && $a->isValid();
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}
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/**
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* @psalm-assert-if-false B $a
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*/
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function isInvalidB(A $a) : bool {
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return $a instanceof B || !$a->isValid();
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}
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function takesA(A $a) : void {
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if (isValidB($a)) {
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$a->bar();
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}
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if (isInvalidB($a)) {
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// do something
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} else {
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$a->bar();
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}
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$a->bar(); //error
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}
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```
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As well as getting Psalm to understand that the given data must be a certain type, you can also show that a variable must be not null:
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```php
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<?php
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/**
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* @psalm-assert !null $value
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*/
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function assertNotNull($value): void {
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// Some check that will mean the method will only complete if $value is not null.
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}
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```
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And you can check on null values:
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```php
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<?php
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/**
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* @psalm-assert-if-true null $value
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*/
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function isNull($value): bool {
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return ($value === null);
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}
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```
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