Naming is hard. This is largely about naming. Ditto, what might std::exchange do?
Exchange two values?
Well …No. Let the code speak. You want left to become right and right to become left, right?
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auto left = "LEFT", right = "RIGHT" ; |
Naturally, you would use something called perhaps exchange, would you? (hint: std:swap is taken)
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std::exchange(left,right); |
Alas. std::exchange is a name, given by a committee. Above does not exchange.
After the call above right is unchanged. Indeed left == right, and there is a return value (for some reason) too.
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// std::exchange calling by the book auto left_previous = std::exchange(left,right); |
To do the exchange by the meaning from the English language, one more call is required
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auto right_previous = std::exchange(right, left_previous ) ; |
Voila, left and right are exchanged!
No wonder people are looking to Rust, Go, Swift and elsewhere. In case you want to stay with C++, be brave and add this function to your library.
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// exchange as the English term "exchange" defines template<typename T> void dbj_exchange(T & a, T & b) { T t = a; a = b ; b = t ; } |
Thinking of it all, perhaps std::exchange is better to be called “assign”? Who knows. Back to dbj_exchange .Usage is daringly simple too:
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auto left = "LEFT", right = "RIGHT" ; dbj_exchange(left,right); |
No SFINAE necessary. In case of the wrong usage, wrong types used, or any similar libertarian activity, you will be punished by the compiler, disproportionately.
