rfc:never_for_parameter_types
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| Both sides previous revisionPrevious revisionNext revision | Previous revisionLast revisionBoth sides next revision |
| rfc:never_for_parameter_types [2021/08/15 07:41] – formatting fix jordanrl | rfc:never_for_parameter_types [2021/08/17 12:33] – argument -> parameter jordanrl |
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| ===== Introduction ===== | ===== Introduction ===== |
| Arguments in PHP are contravariant to preserve Liskov substitution. This means that if class B extends class A, then redefines a function call, the entire type of that argument from class A must be present in the type of the argument in class B: | Parameters in PHP are contravariant to preserve Liskov substitution. This means that if class B extends class A, then redefines a function call, the entire type of that parameter from class A must be present in the type of the parameter in class B: |
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| <code php> | <code php> |
| </code> | </code> |
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| Thus, the more specific a type is for an argument in a base class, the more broad it can be in an extending class with the requirement that it must also include the type from the base class. | Thus, the more specific a type is for an parameter in a base class, the more broad it can be in an extending class with the requirement that it must also include the type from the base class. |
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| Since ''never'' is a bottom type within the PHP engine, all other types contain it. This RFC proposes allowing ''never'' as a valid argument type for functions. | Since ''never'' is a bottom type within the PHP engine, all other types contain it. This RFC proposes allowing ''never'' as a valid parameter type for functions. |
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| ===== Use Cases ===== | ===== Use Cases ===== |
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| ===== References ===== | ===== References ===== |
| * https://github.com/JordanRL/never-argument-type/edit/master/README.md | * https://github.com/JordanRL/never-argument-type/blob/master/README.md |
| * https://en.wikipedia.org/wiki/Covariance_and_contravariance_(computer_science) | * https://en.wikipedia.org/wiki/Covariance_and_contravariance_(computer_science) |
| * https://en.wikipedia.org/wiki/Bottom_type | * https://en.wikipedia.org/wiki/Bottom_type |
rfc/never_for_parameter_types.txt · Last modified: 2021/08/24 11:53 by jordanrl