xp-forge/match

Match DSL

Matching DSL

, _(*1)

Fluent API for matching., _(*2)

Matching

The following outputs two lines, My Team 🔒 and Developers:, _(*3)

Sequence::of([new Group('My Team', Types::$CLOSED), new Group('Developers', Types::$OPEN)])
  ->map((new Match('Group::type'))
    ->when(new IsEqual(Types::$OPEN), function($group) { return $group->name(); })
    ->when(new IsEqual(Types::$CLOSED), function($group) { return $group->name().' 🔒'; })
  )
  ->each('util.cmd.Console::writeLine')
;

If the group's type() method where to return an unhandled group type, e.g. Types::$HIDDEN, an exception would be raised., _(*4)

Unhandled values

To handle the default case, use the otherwise() method:, _(*5)

$match= (new Match('Group::type'))
  ->when(new IsEqual(Types::$OPEN), function($group) { return $group->name(); })
  ->when(new IsEqual(Types::$CLOSED), function($group) { return $group->name().' 🔒'; })
  ->otherwise(function($group) { return $group->name().' ('.$group->type()->name().')'; })
;

Matching values

For the special case of testing equality, we can use the specialized ValueOf matcher:, _(*6)

$kind= (new ValueOf('Event::weekday'))
  ->when(Day::$SATURDAY, function() { return 'Weekend'; })
  ->when(Day::$SUNDAY, function() { return 'Weekend'; })
  ->otherwise(function() { return 'During the week'; })
;

$display= $kind(new Event('Relax', new Date('2015-01-18')));    // `Weekend`
$display= $kind(new Event('Meeting', new Date('2015-01-19')));  // `During the week`

Matching types

The following is a reimplementation of PHP's serialize function (incomplete, but you get the idea):, _(*7)

$serialize= (new TypeOf())
  ->when(Primitive::$INT, function($value) { return 'i:'.$value.';'; })
  ->when(Primitive::$STRING, function($value) { return 's:'.strlen($value).':"'.$value.'";'; })
  ->when(Type::$ARRAY, function($value, $self) {
    $r= 'a:'.sizeof($value).':{';
    foreach ($value as $key => $val) {
      $r.= $self($key).$self($val);
    }
    return $r.'}';
  })
  ->when(null, function() { return 'N;'; })
;

$serialized= $serialize(1);       // `i:1;`
$serialized= $serialize('Test');  // `s:4:"Test";`
$serialized= $serialize([1, 2]);  // `a:2:{i:0;i:1;i:1;i:2;}`
$serialized= $serialize(null);    // `N;`

The Type::$ARRAY is actually a type union consisting of zero-indexed arrays and maps, both of which are known to PHP as an array (in contrast, the XP Framework only speaks of the first as arrays). We use it here for performance reasons since we don't need to distinguish between the two anyways., _(*8)

Performance

They KeyOf class is a high-performance alternative to the ValueOf class although it's restricted to integers and strings (it uses them as keys in its backing map)., _(*9)

// Using native if and comparison
$match= function($value) {
  if (0 === $value) {
    return 'No elements';
  } else if (1 === $value) {
    return 'One element';
  } else {
    return $value.' elements';
  }
};

// Using KeyOf class
$match= (new KeyOf())
  ->when(0, function() { return 'No elements'; })
  ->when(1, function() { return 'One element'; })
  ->otherwise(function($value) { return $value.' elements'; })
;

// Using ValueOf class
$match= (new ValueOf())
  ->when(0, function() { return 'No elements'; })
  ->when(1, function() { return 'One element'; })
  ->otherwise(function($value) { return $value.' elements'; })
;

Using 500000 iterations, PHP 5.4 / Windows 8.1:, _(*10)

Further reading

This library was inspired by Scala's patter matching., _(*11)

• Scala Tour: Pattern Matching
• Instanceof operator and Visitor pattern replacement in Java 8