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Address items called out in Issue 1418 (#1538)

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Zachary Henkel 2019-11-21 13:12:41 -06:00 committed by Herb Sutter
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@ -11981,7 +11981,8 @@ The language already knows the common cases where objects can be moved from, esp
Never write `std::move()` just because you've heard "it's more efficient."
In general, don't believe claims of "efficiency" without data (???).
In general, don't complicate your code without reason (??)
In general, don't complicate your code without reason (??).
Never write `std::move()` on a const object, it is silently transformed into a copy (see Item 23 in [Meyers15](#Meyers15))
##### Example, bad
@ -12021,9 +12022,9 @@ The language already knows that a returned value is a temporary object that can
* Flag use of `std::move(x)` where `x` is an rvalue or the language will already treat it as an rvalue, including `return std::move(local_variable);` and `std::move(f())` on a function that returns by value.
* Flag functions taking an `S&&` parameter if there is no `const S&` overload to take care of lvalues.
* Flag a `std::move`s argument passed to a parameter, except when the parameter type is one of the following: an `X&&` rvalue reference; a `T&&` forwarding reference where `T` is a template parameter type; or by value and the type is move-only.
* Flag a `std::move`s argument passed to a parameter, except when the parameter type is an `X&&` rvalue reference or the type is move-only and the parameter is passed by value.
* Flag when `std::move` is applied to a forwarding reference (`T&&` where `T` is a template parameter type). Use `std::forward` instead.
* Flag when `std::move` is applied to other than an rvalue reference. (More general case of the previous rule to cover the non-forwarding cases.)
* Flag when `std::move` is applied to other than an rvalue reference to non-const. (More general case of the previous rule to cover the non-forwarding cases.)
* Flag when `std::forward` is applied to an rvalue reference (`X&&` where `X` is a concrete type). Use `std::move` instead.
* Flag when `std::forward` is applied to other than a forwarding reference. (More general case of the previous rule to cover the non-moving cases.)
* Flag when an object is potentially moved from and the next operation is a `const` operation; there should first be an intervening non-`const` operation, ideally assignment, to first reset the object's value.