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F.19: s/T&&/TP&&/

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Michael Park 2015-12-11 15:29:21 -05:00
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@ -2342,7 +2342,7 @@ Unique owner types that are move-only and cheap-to-move, such as `unique_ptr`, c
If the object is to be passed onward to other code and not directly used by this function, we want to make this function agnostic to the argument `const`-ness and rvalue-ness.
In that case, and only that case, make the parameter `TP&&` where `TP` is a template type parameter -- it both *ignores* and *preserves* `const`-ness and rvalue-ness. Therefore any code that uses a `T&&` is implicitly declaring that it itself doesn't care about the variable's `const`-ness and rvalue-ness (because it is ignored), but that intends to pass the value onward to other code that does care about `const`-ness and rvalue-ness (because it is preserved). When used as a parameter `TP&&` is safe because any temporary objects passed from the caller will live for the duration of the function call. A parameter of type `TP&&` should essentially always be passed onward via `std::forward` in the body of the function.
In that case, and only that case, make the parameter `TP&&` where `TP` is a template type parameter -- it both *ignores* and *preserves* `const`-ness and rvalue-ness. Therefore any code that uses a `TP&&` is implicitly declaring that it itself doesn't care about the variable's `const`-ness and rvalue-ness (because it is ignored), but that intends to pass the value onward to other code that does care about `const`-ness and rvalue-ness (because it is preserved). When used as a parameter `TP&&` is safe because any temporary objects passed from the caller will live for the duration of the function call. A parameter of type `TP&&` should essentially always be passed onward via `std::forward` in the body of the function.
##### Example