Is it possible to use structured bindings to assign class members?

Question

I\'d like to use C++ 17 structured bindings to assign a value to a class member variable, like this:

#include 
#include 

struct         


        

Answer 1

Use std::tie to assign values to existing objects:

std::tie(result_, error_) = square_root(input);

That's why it was added to C++11. Of course, you'd need to forego using Result in favor of a std::tuple. Which IMO is better for such ad-hoc "return multiple things" scenarios.

Structured bindings are exclusively for declaring new names.

Another approach, which could be even better, since C++1z is on the table, is to not re-invent the wheel. Return a std::optional

auto square_root(double input) {
   return input < 0 ? std::nullopt : std::optional{std::sqrt(input)}; 
}

This has the clear semantics of "there may be a value, or not".

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By the way, unconditionally calling std::sqrt with a negative input is a bad idea. Especially if you don't configure your floating point environment in any special way prior.