rfc:scalar-pseudo-type

Differences

This shows you the differences between two versions of the page.

Link to this comparison view

Next revision		Previous revision
Next revisionBoth sides next revision
rfc:scalar-pseudo-type [2017/12/24 15:20] – created fleshgrinderrfc:scalar-pseudo-type [2017/12/24 17:29] – Added more Examples fleshgrinder
Line 81: Line 81:
  
 The function [[https://php.net/is-scalar|is_scalar]] to determine whether a value is ''scalar'' or not already exist in PHP since a long time and must not be added. The function [[https://php.net/is-scalar|is_scalar]] to determine whether a value is ''scalar'' or not already exist in PHP since a long time and must not be added.
 +
 +====== Examples ======
 +======= Scalar Parameters =======
 +PHP core already contains a multitude of procedures that could be constrained to ''scalar'' instead of ''mixed''.
 +
 +<code php>
 +function strpos(string $haystack, scalar $needle, //...
 +function printf(string $format, scalar ...$args): string {}
 +// ... and many, many, many more ...
 +</code>
 +
 +However, it is also useful in userland.
 +
 +<code php>
 +interface Parser {
 +    /** @return static */
 +    function parse(scalar $input);
 +}
 +</code>
 +
 +<code php>
 +namespace Userland\Database\MySQL;
 +
 +class ReadConnection {
 +    private $mysqli;
 +
 +    function fetch(string $query, ?scalar ...$args): ResultSet {
 +        $types = '';
 +        
 +        foreach ($args as $arg) {
 +            if (is_float($arg)) {
 +                $types .= 'd';
 +            } elseif (is_bool($arg) || is_int($arg)) {
 +                $types .= 'i';
 +            } else {
 +                $types .= 's';
 +            }
 +        }
 +
 +        //...
 +        $stmt->bind_params($types, ...$params);
 +        //...
 +    }
 +}
 +</code>
 +
 +In other words, it allows one to implement type safe method overloading over a well-defined set of types. It does not cover all possibilities just one common one. (Covering all possibilities is not possible anyways and would require union types.)
 +
 +======= Scalar Returns =======
 +The return type constraint is less commonly useful than the one for parameters, however, it is specifically of interest while designing supertypes for others and to work around the magic ''toString'' method that can only return values of type ''string'' (and is incompatible with exceptions).
 +
 +<code php>
 +interface Convertible {
 +    function into(): scalar;
 +}
 +
 +final class Longitude implements Convertible {
 +    /** @var float */
 +    private $deg;
 +    
 +    //...
 +    
 +    function into(): float {
 +        return $this->deg;
 +    }
 +}
 +
 +// In combination with our previous DB example.
 +$db->fetch('SELECT * FROM t WHERE lng = ?', (new Longitude(42.42))->into());
 +</code>
  
 ===== Backward Incompatible Changes ===== ===== Backward Incompatible Changes =====
 ''scalar'' is implemented as reserved name, therefore a class, interface, or trait named ''scalar'' cannot be declared.  ''scalar'' is implemented as reserved name, therefore a class, interface, or trait named ''scalar'' cannot be declared. 
 +
 +===== Open Issues =====
 +  * Whether ''scalar'' should accept objects with a magic ''toString'' method in weak mode like the ''string'' constraint does.
  
 ===== Proposed PHP Version(s) ===== ===== Proposed PHP Version(s) =====
rfc/scalar-pseudo-type.txt · Last modified: 2017/12/24 23:33 by fleshgrinder

Page Tools