Does PHP Utilize Short-Circuit Evaluation in Logical Expressions?

Short-Circuit Evaluation in PHP

This code snippet demonstrates a PHP if statement with multiple conditions connected by the logical AND (&&) operator:

if (is_valid($string) && up_to_length($string) && file_exists($file)) 
{
    ......
}

Does PHP Short-Circuit Evaluation?

Yes, PHP implements short-circuit evaluation for logical operators like && (AND) and || (OR). This means that the interpreter evaluates conditions from left to right, and if the result of the first condition is sufficient to determine the outcome of the entire expression, the remaining conditions are not evaluated.

How PHP Implements Short-Circuit Evaluation

Using the && operator as an example:

1. The interpreter evaluates the first condition, is_valid($string).
2. If is_valid($string) returns false, the expression is automatically evaluated to false, regardless of the other conditions.
3. If is_valid($string) returns true, the interpreter continues to evaluate the second condition, up_to_length($string).
4. Only if both is_valid($string) and up_to_length($string) return true does the interpreter proceed to evaluate file_exists($file).

Why PHP Uses Short-Circuit Evaluation

Short-circuit evaluation helps optimize code performance by reducing unnecessary comparisons. For instance, in the provided example, if is_valid($string) returns false, there's no need to check the remaining conditions, since the overall expression is already false.

Example Demonstration

To illustrate short-circuit evaluation in action:

function saySomething()
{
    echo 'hi!';
    return true;
}

if (false && saySomething())
{
    echo 'statement evaluated to true';
}

The output will be "hi!" even though the second condition in the if statement is never evaluated. This is because

is evaluated first, and since it returns false, the entire expression is false.

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