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| user_guide:extend:polymorphic [2021/01/12 15:38] – external edit 127.0.0.1 | user_guide:extend:polymorphic [2021/01/12 15:46] (current) – [Labels] gawrilow |
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| ===== Labels ===== | ===== Labels ===== |
| Labels allow to provide several alternative implementations for the same function or for a family of functions with compatible signatures. The choice of the function to be called is governed by active preference lists (cf. user commands [[:user_gude:howto:shell_custom#preferences|prefer, prefer_now, show_preferences]]). First, all candidates with the label of the highest rank are considered according to usual overload resolution rules. If none has matched the argument list, the candidates with the label of the next lower rank are considered, and so on. | Labels allow to provide several alternative implementations for the same function or for a family of functions with compatible signatures. The choice of the function to be called is governed by active preference lists (cf. user commands [[:user_guide:howto:shell_custom#preferences|prefer, prefer_now, show_preferences]]). First, all candidates with the label of the highest rank are considered according to usual overload resolution rules. If none has matched the argument list, the candidates with the label of the next lower rank are considered, and so on. |
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| Labels are mandatory for //global methods//. The overload resolution for global methods runs slightly differently from other functions. The application first calls ''$method=Overload::Global:://NAME//(//args//%%...%%)'' to obtain the code reference pointing to the currently preferred method matching the given list of arguments. Then it creates an object of the corresponding class using something like ''%%$object=method_owner($method)->new(...);%%'' or retrieves a suitable object in whatever appropriate way, and finally calls the method, passing the obtained object as a leading argument: ''%%$method->($object, %%//args//%%...);%%'' | Labels are mandatory for //global methods//. The overload resolution for global methods runs slightly differently from other functions. The application first calls ''$method=Overload::Global:://NAME//(//args//%%...%%)'' to obtain the code reference pointing to the currently preferred method matching the given list of arguments. Then it creates an object of the corresponding class using something like ''%%$object=method_owner($method)->new(...);%%'' or retrieves a suitable object in whatever appropriate way, and finally calls the method, passing the obtained object as a leading argument: ''%%$method->($object, %%//args//%%...);%%'' |