# Issue types

### AbstractInstantiation

Emitted when an attempt is made to instatiate an abstract class:

```php
abstract class A {}
new A();
```

### AssignmentToVoid

Emitted when assigning from a function that returns `void`:

```php
function foo() : void {}
$a = foo();
```

### CircularReference

Emitted when a class references itself as one of its parents

```php
class A extends B {}
class B extends A {}
```

### ContinueOutsideLoop

Emitted when encountering a `continue` statement outside a loop context.

### DeprecatedClass

Emitted when creating a new instance of a deprecated class:

```php
/** @deprecated */
class A {}
new A();
```

### DeprecatedMethod

Emitted when calling a deprecated method on a given class:

```php
class A {
    /** @deprecated */
    public function foo() : void {}
}
(new A())->foo();
```

### DeprecatedProperty

Emitted when getting/setting a deprecated property of a given class

```php
class A {
    /**
     * @deprecated
     * @var ?string
     */
    public $foo;
}
(new A())->foo = 5;
```

### DuplicateClass

Emitted when a class is defined twice

```php
class A {}
class A {}
```

### DuplicateParam

Emitted when a function has a param defined twice

```php
function foo(int $b, string $b) {}
```

### EmptyArrayAccess

Emitted when attempting to access a value on an empty array

```php
$a = [];
$b = $a[0];
```

### FalsableReturnStatement

Emitted if a return statement contains a false value, but the function return type does not allow false

```php
function foo() : string {
    if (rand(0, 1)) {
        return "foo";
    }

    return false; // emitted here
}
```

### ForbiddenCode

Emitted when Psalm encounters a var_dump, exec or similar expression that may make your code more vulnerable

```php
var_dump($foo);
```

### ImplementedReturnTypeMismatch

Emitted when a class that inherits another, or implements an interface, has docblock return type that's entirely different to the parent. Subclasses of the parent return type are permitted, in docblocks.

```php
class A {
    /** @return bool */
    public function foo() {
        return true;
    }
}
class B extends A {
    /** @return string */
    public function foo()  {
        return "hello";
    }
}
```

### ImplicitToStringCast

Emitted when implictly converting an object with a `__toString` method to a string

```php
class A {
    public function __toString() {
        return "foo";
    }
}

function takesString(string $s) : void {}

takesString(new A);
```

### InaccessibleClassConstant

Emitted when a public/private class constant is not accessible from the calling context

```php
class A {
    protected const FOO = 'FOO';
}
echo A::FOO;
```

### InaccessibleMethod

Emitted when attempting to access a protected/private method from outside its available scope

```php
class A {
    protected function foo() : void {}
}
echo (new A)->foo();
```

### InaccessibleProperty

Emitted when attempting to access a protected/private property from outside its available scope

```php
class A {
    /** @return string */
    protected $foo;
}
echo (new A)->foo;
```

### InvalidArgument

Emitted when a supplied function/method argument is incompatible with the method signature or docblock one.

```php
class A {}
function foo(A $a) : void {}
foo("hello");
```

### InvalidArrayAccess

Emitted when attempting to access an array offset on a value that does not permit it

```php
$arr = 5;
echo $arr[0];
```

### InvalidArrayAssignment

Emitted when attempting to assign a value on a non-array

```php
$arr = 5;
$arr[0] = 3;
```

### InvalidArrayOffset

Emitted when when attempting to access an array using a value that's not a valid offet for that array

```php
$a = [5, 20, 18];
echo $a["hello"];
```

### InvalidCast

Emitted when attempting to cast a value that's not castable

```php
class A {}
$a = new A();
$b = (string)$a;
```

### InvalidCatch

Emitted when trying to catch a class/interface that doesn't extend `Exception` or implement `Throwable`

```php
class A {}
try {
    $worked = true;
}
catch (A $e) {}
```

### InvalidClass

Emitted when referencing a class with the wrong casing

```php
class Foo {}
(new foo());
```

### InvalidClone

Emitted when trying to clone a value that's not cloneable

```php
$a = "hello";
$b = clone $a;
```

### InvalidDocblock

Emitted when there's an error in a docblock type

```php
/** @var array() */
$a = [];
```

### InvalidFalsableReturnType

Emitted when a function can return a nullable value, but its given return type says otherwise

```php
function foo() : string {
    if (rand(0, 1)) {
        return "foo";
    }

    return false;
}
```

### InvalidFunctionCall

Emitted when calling a function on a non-callable variable

```php
$a = 5;
$b = $a();
```

### InvalidGlobal

Emitted when there's a reference to the global keyword where it's not expected

```php
global $e;
```

### InvalidIterator

Emitted when trying to iterate over a value that's not iterable

```php
$a = 5;
foreach ($a as $b) {}
```

### InvalidMethodCall

Emitted when attempting to call a method on a non-object

```php
$a = 5;
$a->foo();
```

### InvalidNullableReturnType

Emitted when a function can return a nullable value, but its given return type says otherwise

```php
function foo() : string {
    if (rand(0, 1)) {
        return "foo";
    }

    return null;
}
```

### InvalidOperand

Emitted when using something as an operand that is unexected

```php
class A {}
echo (new A) . ' ';
```

### InvalidParamDefault

Emitted when a function parameter default clashes with the type Psalm expects the param to be

```php
function foo(int $i = false) : void {}
```

### InvalidPassByReference

Emitted when passing a non-variable to a function that expects a by-ref variable

```php
function foo(array &$arr) : void {}
foo([0, 1, 2]);
```

### InvalidPropertyAssignment

Emitted when attempting to assign a property to a non-object

```php
$a = "foo";
$a->bar = "bar";
```

### InvalidPropertyFetch

Emitted when attempting to get a property from a non-object

```php
$a = "foo";
echo $a->bar;
```

### InvalidReturnStatement

Emitted when a function return statement is incorrect

```php
function foo() : string {
    return 5; // emitted here
}
```

### InvalidReturnType

    Emitted when a function’s signature return type is incorrect (often emitted with `InvalidReturnStatement`)

```php
function foo() : int {
    if (rand(0, 1)) {
        return "hello";
    }

    return 5;
}
```

### InvalidScalarArgument

Emitted when a scalar value is passed to a method that expected another scalar type

```php
function foo(int $i) : void {}
function bar(string $s) : void {
    if (is_numeric($s)) {
        foo($s);
    }
}
```

### InvalidScope

Emitted when referring to `$this` outside a class

```php
echo $this;
```

### InvalidStaticInvocation

Emitted when trying to call an instance function statically

```php
class A {
    /** @var ?string */
    public $foo;

    public function bar() : void {
        echo $this->foo;
    }
}

A::bar();
```

### InvalidThrow

Emitted when trying to throw a class that doesn't extend `Exception` or implement `Throwable`

```php
class A {}
throw new A();
```

### InvalidToString

Emitted when a `__toString` method does not always return a `string`

```php
class A {
    public function __toString() {
        return true;
    }
}
```

### LessSpecificReturnStatement

Emitted when a return statement is more general than the return type given for the function

```php
class A {}
class B extends A {}

function foo() : B {
    return new A(); // emitted here
}
```

### LessSpecificReturnType

Emitted when a return type covers more possibilities than the function itself

```php
function foo() : ?int {
    return 5;
}
```

### LoopInvalidation

Emitted when logic inside a loop invalidates one of the conditionals of the loop

```php
for ($i = 0; $i < 10; $i++) {
    $i = 5;
}
```

### MethodSignatureMismatch

Emitted when a method parameter differs from a parent method parameter, or if there are fewer parameters than the parent method

```php
class A {
    public function foo(int $i) : void {}
}
class B extends A {
    public function foo(string $s) : void {}
}
```

### MismatchingDocblockParamType

Emitted when an `@param` entry in a function’s docblock doesn’t match the param typehint,

```php
class A {}
class B {}
/**
 * @param B $b // emitted here
 */
function foo(A $b) : void {}
```

This, however, is fine:

```php
class A {}
class B extends A {}
/**
 * @param B
 */
function foo(A $b) : void {}
```

### MismatchingDocblockReturnType

Emitted when an `@return` entry in a function’s docblock doesn’t match the function return typehint

```php
class A {}
class B {}
/**
 * @return B // emitted here
 */
function foo() : A {
    return new A();
}
```

This, however, is fine:

```php
class A {}
class B extends A {}
/**
 * @return B // emitted here
 */
function foo() : A {
    return new B();
}
```

### MismatchingDocblockParamType

Emitted when an `@param` entry in a function’s docblock doesn’t match the param typehint

```php
/**
 * @param int $b 
 */
function foo(string $b) : void {}
```

### MisplacedRequiredParam

Emitted when a required param is before a param that is not required. Included in Psalm because it is an E_WARNING in PHP

```php
function foo(int $i = 5, string $j) : void {}
```

### MissingClosureParamType

Emitted when a closure paramter has no type information associated with it

```php
$a = function($a): string {
    return "foo";
};
```

### MissingClosureReturnType

Emitted when a closure lacks a return type

```php
$a = function() {
    return "foo";
};
```

### MissingConstructor

Emitted when non-null properties without default values are defined in a class without a `__construct` method

```php
class A {
    /** @var string */
    public $foo;
}
```

### MissingDocblockType

Emitted when a docblock is present, but the type is missing or badly formatted

```php
/** @var $a */
$a = [];
```

### MissingFile

Emitted when using `include` or `require` on a file that does not exist

```php
require("nonexistent.php");
```

### MissingParamType

Emitted when a function paramter has no type information associated with it

```php
function foo($a) : void {}
```

### MissingPropertyType

Emitted when a property is defined on a class without a type

```php
class A {
    public $foo;
}
```

### MissingReturnType

Emitted when a function doesn't have a return type defined

```php
function foo() {
    return "foo";
}
```

### MixedArgument

Emitted when Psalm cannot determine the type of an argument

```php
function takesInt(int $i) : void {}
takesInt($_GET['foo']);
```

### MixedArrayAccess

Emitted when trying to access an array offset on a value whose type Psalm cannot determine

```php
echo $_GET['foo'][0];
```

### MixedArrayAssignment

Emitted when trying to assign a value to an array offset on a value whose type Psalm cannot determine

```php
$_GET['foo'][0] = "5";
```

### MixedArrayOffset

Emitted when attempting to access an array offset where Psalm cannot determine the offset type

```php
echo [1, 2, 3][$_GET['foo']];
```

### MixedAssignment

Emitted when assigning a variable to a value for which Psalm cannot infer a type

```php
$a = $_GET['foo'];
```

### MixedInferredReturnType

Emitted when Psalm cannot determine a function's return type

```php
function foo() : int {
    return $_GET['foo'];
}
```

### MixedMethodCall

Emitted when calling a method on a value that Psalm cannot infer a type for

```php
/** @param mixed $a */
function foo($a) : void {
    $a->foo();
}
```

### MixedOperand

Emitted when Psalm cannot infer a type for an operand in any calculated expression

```php
echo $_GET['foo'] + "hello";
```

### MixedPropertyAssignment

Emitted when assigning a property to a value for which Psalm cannot infer a type

```php
/** @param mixed $a */
function foo($a) : void {
    $a->foo = "bar";
}
```

### MixedPropertyFetch

Emitted when retrieving a property on a value for which Psalm cannot infer a type

```php
/** @param mixed $a */
function foo($a) : void {
    echo $a->foo;
}
```

### MixedReturnStatement

Emitted when Psalm cannot determine the type of a given return statement

```php
function foo() : int {
    return $_GET['foo']; // emitted here
}
```

### MixedStringOffsetAssignment

Emitted when assigning a value on a string using a value for which Psalm cannot infer a type

```php
"hello"[0] = $_GET['foo'];
```

### MixedTypeCoercion

Emitted when Psalm cannot be sure that part of an array/iterabble argument's type constraints can be fulfilled

```php
function foo(array $a) : void {
    takesStringArray($a);
}

/** @param string[] $a */
function takesStringArray(array $a) : void {}
```

### MoreSpecificImplementedReturnType

Emitted when a class implements an interface method but its return type is less specific than the interface method return type

```php
class A {}
class B extends A {}
interface I {
    /** @return B[] */
    public function foo();
}
class D implements I {
    /** @return A[] */
    public function foo() {
        return [new A, new A];
    }
}
```

### MoreSpecificReturnType

Emitted when the declared return type for a method is more specific than the inferred one (emitted in the same methods that `LessSpecificReturnStatement` is)

```php
class A {}
class B extends A {}
function foo() : B {
    /** @psalm-suppress LessSpecificReturnStatement */
    return new A();
}
```

### NoInterfaceProperties

Emitted when trying to fetch a property on an interface as interfaces, by definition, do not have definitions for properties.

```php
interface I {}
class A implements I {
    /** @var ?string */
    public $foo;
}
function bar(I $i) : void {
    if ($i->foo) {}
}
```

### NonStaticSelfCall

Emitted when calling a non-static function statically

```php
class A {
    public function foo(): void {}

    public function bar(): void {
        self::foo();
    }
}
```

### NullableReturnStatement

Emitted if a return statement contains a null value, but the function return type is not nullable

```php
function foo() : string {
    if (rand(0, 1)) {
        return "foo";
    }

    return null; // emitted here
}
```

### NullArgument

Emitted when calling a function with a null value argument when the function does not expect it

```php
function foo(string $s) : void {}
foo(null);
```

### NullArrayAccess

Emitted when trying to access an array value on `null`

```php
$arr = null;
echo $arr[0];
```

### NullArrayOffset

Emitted when trying to access an array offset with `null`

```php
$arr = ['' => 5, 'foo' => 1];
echo $arr[null];
```

### NullFunctionCall

Emitted when trying to use `null` as a `callable`

```php
$arr = null;
echo $arr();
```

### NullIterator

Emitted when iterating over `null`

```php
foreach (null as $a) {}
```

### NullOperand

Emitted when using `null` as part of an operation (e.g. `+`, `.`, `^` etc.`)

```php
echo null . 'hello';
```

### NullPropertyAssignment

Emitted when trying to set a property on `null`

```php
$a = null;
$a->foo = "bar";
```

### NullPropertyFetch

Emitted when trying to fetch a property on a `null` value

```php
$a = null;
echo $a->foo;
```

### NullReference

Emitted when attempting to call a method on `null`

```php
$a = null;
$a->foo();
```

### OverriddenMethodAccess

Emitted when a method is less accessible than its parent

```php
class A {
    public function foo() : void {}
}
class B extends A {
    protected function foo() : void {}
}
```

### ParadoxicalCondition

Emitted when a paradox is encountered in your programs logic that could not be caught by `RedundantCondition`

```php
function foo(?string $a) : ?string {
    if ($a) return $a;
    if ($a) echo "cannot happen";
}
```

### ParentNotFound

Emitted when using `parent::` in a class without a parent class.

```php
class A {
  public function foo() : void {
    parent::foo();
  }
}
```

### PossiblyFalseArgument

Emitted when a function argument is possibly `false`, but the function doesn’t expect `false`. This is distinct from a function argument is possibly `bool`, which results in `PossiblyInvalidArgument`.

```php
function foo(string $s) : void {
    $a_pos = strpos($s, "a");
    echo substr($s, $a_pos);
}
```

### PossiblyFalseReference

Emitted when making a method call on a value than might be `false`

```php
class A {
    public function bar() : void {}
}

/** @return A|false */
function foo() {
    return rand(0, 1) ? new A : false;
}

foo()->bar();
```

### PossiblyInvalidArgument

Emitted when

```php
/** @return int|stdClass */
function foo() {
    return rand(0, 1) ? 5 : new stdClass;
}
function bar(int $i) : void {}
bar(foo());
```

### PossiblyInvalidArrayAccess

Emitted when attempting to access an array offset on a value that may not be an array

```php
$arr = rand(0, 1) ? 5 : [4, 3, 2, 1];
echo $arr[0];
```

### PossiblyInvalidArrayAssignment

Emitted when attempting to assign an array offset on a value that may not be an array

```php
$arr = rand(0, 1) ? 5 : [4, 3, 2, 1];
$arr[0] = "hello";
```

### PossiblyInvalidArrayOffset

Emitted when it’s possible that the array offset is not applicable to the value you’re trying to access.

```php
$arr = rand(0, 1) ? ["a" => 5] : "hello";
echo $arr[0];
```

### PossiblyInvalidFunctionCall

Emitted when trying to call a function on a value that may not be callable

```php
$a = rand(0, 1) ? 5 : function() : int { return 5; };
$b = $a();
```

### PossiblyInvalidMethodCall

Emitted when trying to call a method on a value that may not be an object

```php
class A {
    public function bar() : void {}
}

/** @return A|int */
function foo() {
    return rand(0, 1) ? new A : 5;
}

foo()->bar();
```

### PossiblyInvalidPropertyAssignment

Emitted when trying to assign a property on a value that may not be an object or may be an object that doesn’t have the desired property.

```php
class A {
    /** @var ?string */
    public $bar;
}

/** @return A|int */
function foo() {
    return rand(0, 1) ? new A : 5;
}

$a = foo();
$a->bar = "5";
```

### PossiblyInvalidPropertyFetch

Emitted when trying to fetch a property on a value that may not be an object or may be an object that doesn’t have the desired property.

```php
class A {
    /** @var ?string */
    public $bar;
}

/** @return A|int */
function foo() {
    return rand(0, 1) ? new A : 5;
}

$a = foo();
echo $a->bar;
```

### PossiblyNullArgument

Emitted when calling a function with a value that’s possibly null when the function does not expect it

```php
function foo(string $s) : void {}
foo(rand(0, 1) ? "hello" : null);
```

### PossiblyNullArrayAccess

Emitted when trying to access an array offset on a possibly null value

```php
function foo(?array $a) : void {
    echo $a[0];
}
```

### PossiblyNullArrayAssignment

Emitted when trying to set a value on a possibly null array

```php
$a = null;
$a[0][] = 1;
```

### PossiblyNullArrayOffset

Emitted when trying to access a value on an array using a possibly null offset

```php
function foo(?int $a) : void {
    echo [1, 2, 3, 4][$a];
}
```

### PossiblyNullFunctionCall

Emitted when trying to call a function on a value that may be null

```php
function foo(?callable $a) : void {
    $a();
}
```

### PossiblyNullIterator

Emitted when trying to iterate over a value that may be null

```php
function foo(?array $arr) : void {
    foreach ($arr as $a) {}
}
```

### PossiblyNullOperand

Emitted when using a possibly `null` value as part of an operation (e.g. `+`, `.`, `^` etc.`)

```php
function foo(?int $a) : void {
    echo $a + 5;
}
```

### PossiblyNullPropertyAssignment

Emitted when trying to assign a property to a possibly null object

```php
class A {
    /** @var ?string */
    public $foo;
}
function foo(?A $a) : void {
    $a->foo = "bar";
}
```

### PossiblyNullPropertyFetch

Emitted when trying to fetch a property on a possibly null object

```php
class A {
    /** @var ?string */
    public $foo;
}
function foo(?A $a) : void {
    echo $a->foo;
}
```

### PossiblyNullReference

Emitted when trying to call a method on a possibly null value

```php
class A {
    public function bar() : void {}
}
function foo(?A $a) : void {
    $a->bar();
}
```

### PossiblyUndefinedGlobalVariable

Emitted when trying to access a variable in the global scope that may not be defined

```php
if (rand(0, 1)) {
  $a = 5;
}
echo $a;
```

### PossiblyUndefinedMethod

Emitted when trying to access a method that may not be defined on the object

```php
class A {
    public function bar() : void {}
}
class B {}

$a = rand(0, 1) ? new A : new B;
$a->bar();
```

### PossiblyUndefinedVariable

Emitted when trying to access a variable in function scope that may not be defined

```php
function foo() : void {
    if (rand(0, 1)) {
        $a = 5;
    }
    echo $a;
}
```

### PossiblyUnusedMethod

Emitted when `--find-dead-code` is turned on and Psalm cannot find any calls to a given class method

```php
class A {
    public function foo() : void {}
    public function bar() : void {}
}
(new A)->foo();
```

### PossiblyUnusedParam

Emitted when `--find-dead-code` is turned on and Psalm cannot find any uses of a particular parameter in a public/protected method

```php
class A {
    public function foo(int $a, int $b) : int {
        return $a + 4;
    }
}

$a = new A();
$a->foo(1, 2);
```

### PropertyNotSetInConstructor

Emitted when a non-null property without a default value is declared but not set in the class’s constructor

```php
class A {
    /** @var string */
    public $foo;

    public function __construct() {}
}
```

### RawObjectIteration

Emitted when iterating over an object’s properties. This issue exists because it may be undesired behaviour (e.g. you may have meant to iterate over an array)

```php
class A {
    /** @var string|null */
    public $foo;

    /** @var string|null */
    public $bar;
}

function takesA(A $a) {
    foreach ($a as $property) {}
}
```

### RedundantCondition

Emitted when conditional is redundant given previous assertions

```php
class A {}
function foo(?A $a) : ?A {
    if ($a) return $a;
    if ($a) echo "cannot happen";
}
```

### ReferenceConstraintViolation

Emitted when changing the type of a pass-by-reference variable

```php
function foo(string &$a) {
    $a = 5;
}
```

### ReservedWord

Emitted when using a reserved word as a class name

```php
function foo(resource $res) : void {}
```

### TooFewArguments

Emitted when calling a function with fewer arguments than the function has parameters

```php
function foo(string $a) : void {}
foo();
```

### TooManyArguments

Emitted when calling a function with more arguments than the function has parameters

```php
function foo(string $a) : void {}
foo("hello", 4);
```

### TypeCoercion

Emitted when calling a function with an argument which has a less specific type than the function expects

```php
class A {}
class B extends A {}

function takesA(A $a) : void {
    takesB($a);
}
function takesB(B $b) : void {}
```

### TypeDoesNotContainNull

Emitted when checking a non-nullable type for `null`

```php
$a = "hello";
if ($a === null) {}
```

### TypeDoesNotContainType

Emitted checking whether one value has a type or value that is impossible given its currently-known type

```php
$a = "hello";
if ($a === 5) {}
```

### UndefinedClass

Emitted when referencing a class that doesn’t exist

```php
$a = new A();
```

### UndefinedConstant

Emitted when referencing a constant that doesn’t exist

```php
echo FOO_BAR;
```

### UndefinedFunction

Emitted when referencing a function that doesn't exist

```php
foo();
```

### UndefinedGlobalVariable

Emitted when referencing a variable that doesn't exist

```php
echo $a;
```

### UndefinedMethod

Emitted when calling a method that doesn’t exist

```php
class A {}
A::foo();
```

### UndefinedPropertyAssignment

Emitted when assigning a property on an object that doesn’t have that property defined

```php
class A {}
$a = new A();
$a->foo = "bar";
```

### UndefinedPropertyFetch

Emitted when getting a property on an object that doesn’t have that property defined

```php
class A {}
$a = new A();
echo $a->foo;
```

### UndefinedThisPropertyAssignment

Emitted when assigning a property on an object in one of that object’s methods when no such property exists

```php
class A {
    function foo() {
        $this->foo = "bar";
    }
}
```

### UndefinedThisPropertyFetch

Emitted when getting a property for an object in one of that object’s methods when no such property exists

```php
class A {
    function foo() {
        echo $this->foo;
    }
}
```

### UndefinedTrait

Emitted when referencing a trait that doesn’t exist

```php
class A {
    use T;
}
```

### UndefinedVariable

Emitted when referencing a variable that doesn't exist in a given function’s scope

```php
function foo() {
    echo $a;
}
```

### UnevaluatedCode

Emitted when `--find-dead-code` is turned on and Psalm encounters code that will not be evaluated

```php
function foo() : void {
    return;
    $a = "foo";
}
```

### UnimplementedAbstractMethod

Emitted when a class extends another, but does not implement all of its abstract methods

```php
abstract class A {
    abstract public function foo();
}
class B extends A {}
```

### UnimplementedInterfaceMethod

Emitted when a class `implements` an interface but does not implement all of its methods

```php
interface I {
    public function foo();
}
class A implements I {}
```

### UnrecognizedExpression

Emitted when Psalm encounters an expression that it doesn't know how to handle. This should never happen.

### UnrecognizedStatement

Emitted when Psalm encounters a code construct that it doesn't know how to handle. This should never happen.

### UnresolvableInclude

Emitted when Psalm cannot figure out what specific file is being included/required by PHP.

```php
function requireFile(string $s) : void {
    require_once($s);
}
```

### UnusedClass

Emitted when `--find-dead-code` is turned on and Psalm cannot find any uses of a given class

```php
class A {}
class B {}
$a = new A();
```

### UnusedMethod

Emitted when `--find-dead-code` is turned on and Psalm cannot find any uses of a given private method or function

```php
class A {
    public function __construct() {
        $this->foo();
    }
    private function foo() : void {}
    private function bar() : void {}
}
$a = new A();
```

### UnusedParam

Emitted when `--find-dead-code` is turned on and Psalm cannot find any uses of a particular parameter in a private method or function

```php
function foo(int $a, int $b) : int {
    return $a + 4;
}
```

### UnusedVariable

Emitted when `--find-dead-code` is turned on and Psalm cannot find any references to a variable, once instantiated

```php
function foo() : void {
    $a = 5;
    $b = 4;
    echo $b;
}
```