Why Can\'t I Use a Function\'s Return Value Directly in an `if` Statement?

Function Return Values in Write Contexts

Problem:

Encountering an error stating "Can't use function return value in write context" when using functions inside if-statements.

Root Cause:

The error occurs when attempting to use the return value of a function as a condition in a write context, such as an if-statement or assignment operator.

Example:

if (is_string(get_text())) {
    // ...
}

Here, the is_string() function returns a boolean value, which cannot be used directly in a write context like an if-statement.

Solution:

To resolve this issue, use a comparison operator to check the return value:

if (is_string(get_text()) === true) {
    // ...
}

Additional Information:

• This restriction also applies to other language constructs that require a boolean context, such as while and do-while loops.
• It is not limited to functions but also applies to other constructs that return non-boolean values, such as arrays and objects (except for empty arrays and objects, which evaluate to false).
• In PHP 5.5 and later, some language constructs have been relaxed to allow for more flexible use of non-boolean values. However, it is still good practice to use comparison operators when dealing with function return values in write contexts.

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