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| rfc:generics [2016/04/20 08:56] – Fix mistake in traits, add draft section for nested types orolyn | rfc:generics [2016/04/25 15:19] – mindplay |
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| Any valid PHP type-hint may be used as an upper bound, including simple types like ''int'', ''float'', ''bool'', ''string'' and ''object''. (Omission of an upper bound effectively means ''mixed'' in general PHP terms, though we are not proposing the ability to explicitly type-hint as ''mixed'', which isn't supported by PHP.) | Any valid PHP type-hint may be used as an upper bound, including simple types like ''int'', ''float'', ''bool'', ''string'' and ''object''. (Omission of an upper bound effectively means ''mixed'' in general PHP terms, though we are not proposing the ability to explicitly type-hint as ''mixed'', which isn't supported by PHP.) |
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| Note that the choice of the keyword ''is'' to indicate upper bounds is based on the rejection of perhaps more obvious alternatives - repurposing the ''extends'' or ''implements'' keywords would be misleading, since they would work precisely the same way; worse, permitting both keywords would render consumer code invalid if an upper bound type provided by a library is refactored between class and interface. Repurposing ''instanceof'' would also be misleading, since the upper bound is checking the type-hint, not an instance. | Note that the choice of the keyword ''is'' to indicate upper bounds is based on the rejection of perhaps more obvious alternatives - repurposing the ''extends'' or ''implements'' keywords would be misleading, since they would work precisely the same way; worse, permitting both keywords would render consumer code invalid if an upper bound type provided by a library is refactored between class and interface. Repurposing ''instanceof'' would also be misleading, since the upper bound is checking the type-hint, not an instance. Furthermore, we don't want this to collide with possible future mixed scalar types, such as ''number'' or ''scalar'', neither of which make sense in conjunction with either ''extends'' or ''implements''. (If a reserved ''is'' keyword is undesirable for other reasons, a simple '':'' is likely a better alternative than overloading the meaning of an existing keyword.) |
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| == Bounds Checking == | == Bounds Checking == |
| |
| The same applies when overriding constructors and static methods. | The same applies when overriding constructors and static methods. |
| | |
| | ==== Generic Constructors ==== |
| | |
| | Constructors may accept arbitrary type-arguments, just like any other method, e.g.: |
| | |
| | <code php> |
| | class Hello<T1> |
| | { |
| | public function __construct<T1,T2>() |
| | { |
| | // ... |
| | } |
| | } |
| | </code> |
| | |
| | In other words, the constructor may accept more type-arguments than those affecting the type. |
| |
| ==== Generic Closures ==== | ==== Generic Closures ==== |
| |
| TODO: decide whether or not [[https://en.wikipedia.org/wiki/Bounded_quantification|bounded polymorphism]] should be supported. | TODO: decide whether or not [[https://en.wikipedia.org/wiki/Bounded_quantification|bounded polymorphism]] should be supported. |
| | |
| | === Multiple Constraints === |
| | |
| | TODO: decide whether or not multiple constraints should be supported, e.g. with a Java-like syntax: |
| | |
| | <code php> |
| | class A<T> where T is T1, T is T2 { |
| | // ... |
| | } |
| | </code> |
| | |
| | This may relate to the [[https://wiki.php.net/rfc/union_types|union types RFC]] - if implemented, it may be more natural to expect support for union types as bounds. |
| |
| ==== Autoloading ==== | ==== Autoloading ==== |