psalm/docs/running_psalm/issues/MixedMethodCall.md

MixedMethodCall

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

<?php

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

function callFoo(array $arr) : void {
    array_pop($arr)->foo(); // MixedMethodCall emitted here
}

callFoo(
    [new A()]
);

Why this is bad

If Psalm does not know what array_pop($arr) is, it can't verify whether array_pop($arr)->foo() will work or not.

How to fix

Make sure that to provide as much type information as possible to Psalm so that it can perform inference. For example, you could add a docblock to the callFoo function:

<?php

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

/**
 * @param  array<A> $arr
 */
function callFoo(array $arr) : void {
    array_pop($arr)->foo(); // MixedMethodCall emitted here
}

callFoo(
    [new A()]
);

Alternatively you could add a runtime check:

<?php

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

function callFoo(array $arr) : void {
    $a = array_pop($arr);
    assert($a instanceof A);
    $a->foo(); // MixedMethodCall emitted here
}

callFoo(
    [new A()]
);