Is operator for PHP

Plugin for the XP Compiler which adds an is operator to the PHP language compatible with the PHP pattern matching RFC.

Before

A mix of operators, functions, syntax and XP core functionality is():

is_string($value)                                  // for primitives, use is_[T]()
is_callable($value)                                // for pseudo types callable, array, object
is_array($value) || $value instanceof \Traversable // no is_iterable in PHP 5 and 7.0 
$value instanceof Date                             // for value types
null === $value || is_int($value)                  // nullable types cannot be tested directly
is('[:string]', $value)                            // for types beyond PHP type system
is('string|util.URI', $value)                      // for types beyond PHP type system

After

Anything that works as a parameter, property or return type can be used with the is operator.

$value is string
$value is callable
$value is iterable
$value is Date
$value is ?int
$value is array<string, string>
$value is string|URI

Literal patterns

Tests using the identity comparison:

$value is 'test';
$value is 5;
$value is 3|5|null;
$value is 'heart'|'spade';
$value is self::Wild;
$value is 'heart'|'spade'|self::Wild;

Numeric comparison patterns

With greater than (or equal) as well as less than (or equal) operators.

$value is <10;
$value is >=5;
$value is >5 & <10;

Structural patterns

Objects:

$value is Point(x: 3);      // Matches any Point whose $x property is 3
$value is Point(x: 4|5);    // Matches any Point whose $x property is 4 or 5
$value is Point(y: 3)|null; // Matches any Point whose $y property is 3, allowing `null`
$value is Point(y: >0);     // Matches any Point whose $x property is greater than 0

Arrays:

$value is [1, 2, 3, 4];     // Exact match
$value is [1, 2, 3, ...];   // Begins with 1, 2, 3, but may have other entries
$value is [1, 2, mixed, 4]; // Allows any value in the 3rd position
$value is [1, 2, 3|4, 5];   // 3rd value may be 3 or 4

Maps:

$value is ['a' => 'A', 'b' => 'B']; // Exact key/value match, but order doesn't matter
$value is ['b' => 'B', ...];        // Must have a 'b' key with value 'B', and more
$value is ['b' => mixed, ...];      // Must have a 'b' key with any value, and more

Capturing values

Binding variables to object properties as well as array and map values:

$value is Point(x: 3, y: $y);           // If $p->x === 3, bind $p->y to $y
$value is ['a' => 'A', 'b' => $b];      // Bind value of key 'b' to $b
$value is ['op' => 'drop', ... $items]; // Bind rest of array to $items

Match statement

The operator can be used in the cases of a match statement:

$result= match ($value) {
  is int    => $value,
  is string => '"'.strtr($value, ['"' => '\\"']).'"',
  null      => 'null',
};

Installation

After installing the XP Compiler into your project, also include this plugin.

$ composer require xp-framework/compiler
# ...

$ composer require xp-lang/php-is-operator
# ...

No further action is required.

See also

• https://wiki.php.net/rfc/pattern-matching
• https://docs.hhvm.com/hack/expressions-and-operators/is
• https://kotlinlang.org/docs/reference/typecasts.html
• https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/is
• https://externals.io/message/120655 (Proposal to introduce is operator)