rfc:protectedlookup
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rfc:protectedlookup [2008/06/01 11:11] – robinf | rfc:protectedlookup [2008/06/03 13:52] – robinf | ||
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* Date: 2008-06-01 | * Date: 2008-06-01 | ||
* Author: Robin Fernandes < | * Author: Robin Fernandes < | ||
+ | * First Published at: http:// | ||
* Status: in the works | * Status: in the works | ||
Line 217: | Line 218: | ||
* The protected modifier loses its intuitive/ | * The protected modifier loses its intuitive/ | ||
| | ||
+ | |||
==== Option 3 ==== | ==== Option 3 ==== | ||
This approach is similar to option 2, but modifies the new rule slightly so as to preserve the intuitive meaning of the protected modifier. Lookups of protected members on sibling classes fall back to the declaration from the common ancestor class, if available. To illustrate: | This approach is similar to option 2, but modifies the new rule slightly so as to preserve the intuitive meaning of the protected modifier. Lookups of protected members on sibling classes fall back to the declaration from the common ancestor class, if available. To illustrate: | ||
Line 248: | Line 250: | ||
=== Cons === | === Cons === | ||
* Non-trivial code change | * Non-trivial code change | ||
- | * Possibly confusing at first, as code that reads C1::f() may in fact result in an invocation of P::f(). | + | * Possibly confusing at first, as code that reads C1::f() may in fact result in an invocation of P:: |
+ | <code php> | ||
+ | <?php | ||
+ | // Class P declares some private members. | ||
+ | class P { | ||
+ | private function f() { echo ' | ||
+ | public static function test() { | ||
+ | $c = new C; | ||
+ | $c-> | ||
+ | } | ||
+ | } | ||
+ | |||
+ | // Class C1 re-declares the " | ||
+ | class C extends P { | ||
+ | private function f() { echo ' | ||
+ | } | ||
+ | P::test(); | ||
+ | ?> | ||
+ | </ | ||
+ | |||
+ | |||
+ | |||
+ | |||
+ | ===== Appendix ===== | ||
+ | ==== Other potential LSP violations ==== | ||
+ | If Option 1 is rejected on the grounds of a breach of LSP, then other arguable violations of LSP should be reviewed too. | ||
+ | Below is a list of examples to be considered. | ||
+ | === Private static methods === | ||
+ | <code php> | ||
+ | <?php | ||
+ | class P { | ||
+ | | ||
+ | | ||
+ | |||
+ | | ||
+ | $class = get_class($liskov); | ||
+ | echo " | ||
+ | $liskov-> | ||
+ | echo " | ||
+ | $class:: | ||
+ | } | ||
+ | } | ||
+ | |||
+ | class C extends P { | ||
+ | | ||
+ | | ||
+ | } | ||
+ | |||
+ | P::test(new P); | ||
+ | P::test(new C); // Valid Liskov substitution - should this fail? | ||
+ | ?> | ||
+ | </ | ||
+ | === Private static properties === | ||
+ | <code php> | ||
+ | <?php | ||
+ | class P { | ||
+ | | ||
+ | | ||
+ | |||
+ | | ||
+ | $class = get_class($liskov); | ||
+ | echo " | ||
+ | echo $liskov-> | ||
+ | echo " | ||
+ | echo $class::$sa . " | ||
+ | } | ||
+ | } | ||
+ | |||
+ | class C extends P { | ||
+ | | ||
+ | | ||
+ | } | ||
+ | |||
+ | P::test(new P); | ||
+ | P::test(new C); // Valid Liskov substitution - should this fail? | ||
+ | ?> | ||
+ | </ |
rfc/protectedlookup.txt · Last modified: 2017/09/22 13:28 by 127.0.0.1