Side Effect¶
A side effect refers to any change in the state of a program or system that occurs when a function or expression is evaluated, beyond simply returning a value. Side effects are actions that affect something outside the function’s scope, such as modifying a global variable, reading or writing in database, files or any remote API, display data, modify environment.
Side effects are a concept of programming in general. It is important in functional programming, where function without a side effect are called pure.
Side effect has also the literal meaning of a consequence to an action or a situation, similar to collateral.
<?php
// A pure function, with no side effect
function foo($a, $b) {
return $a + $b;
}
// An impure function
function goo($a, $b) {
echo $a;
}
?>
Related : Pure Function, Functional Programming, Determinism, Event Sourcing, Impure Function
Related packages : staabm/side-effects-detector
