Switch Statement in

About Switch Statement

The switch statement facilitates an if..elseif..else conditional control structure.

function getMessage(string $letter): string
{
  switch ($letter) {
    case 'a':
      $message = 'First letter of the english alphabet';
      break;
    case 'z':
      $message = 'Last letter of the english alphabet';
      break;
    case 'l':
    default:
      $message = 'A letter, neither the first nor the last of the alphabet';
  }
  return $message;
}

// getMessage('a') => 'First letter of the english alphabet'
// getMessage('z') => 'Last letter of the english alphabet'
// getMessage('l') => 'A letter, neither the first nor the last of the alphabet'
// getMessage('k') => 'A letter, neither the first nor the last of the alphabet'

One unique feature about switch statements is the "fall-through" behaviour of each case. Note in the example the specific placement of the break statements. Without a break statement, the each case will be executed from the start of the first case until a break statement is evaluated. The order of the case statements inside of a switch is important as only up to the first matching case will be evaluated.

A word of warning: The "fall-through" behaviour facilitates sharing code between similar cases, though it can also be a source of unintended behaviour and bugs if the break statement is forgotten.

Each case performs a non-strict (loose) comparison:

function matches($value): string
{
  switch ($value) {
    case false:
      return 'matches false';
    case true:
      return 'matches true';
  }
}

// matches([]) => 'matches false'
// matches(0) => 'matches false'
// matches(null) => 'matches false'
// matches('') => 'matches false'

// matches([1]) => 'matches true'
// matches(1) => 'matches true'
// matches('a') => 'matches true'

Break-less Switch Pattern

Suppose the example function above is re-written:

function getMessage(string $letter): string
{
  switch ($letter) {
    case 'a':
      return 'First letter of the english alphabet';
    case 'z':
      return 'Last letter of the english alphabet';
    case 'l':
    default:
      return 'A letter, neither the first nor the last of the alphabet';
  }
}

// getMessage('a') => 'First letter of the english alphabet'
// getMessage('z') => 'Last letter of the english alphabet'
// getMessage('l') => 'A letter, neither the first nor the last of the alphabet'
// getMessage('k') => 'A letter, neither the first nor the last of the alphabet'

The behaviour of the function remains the same, but returning directly from the switch statement avoids the possible omission of the break statement.

Conditional Expression Switch Pattern

Another pattern of using the switch statement is to compare each case using an expression:

function compareSum(int $sum): string
{
  switch (true) {
    case $sum < 10:
      return 'Less than 10';
    case $sum > 10:
      return 'More than 10';
    default:
      return 'Sum is 10';
  }
}

This provides some flexibility to write more varied expressions and compose functions when evaluating which case branch to execute.