Fix uses of structured bindings to conform to C++17 standard and appe…

[neboat]

…ase Clang. For discussion on this topic, see https://stackoverflow.com/questions/46114214/lambda-implicit-capture-fails-with-variable-declared-from-structured-binding.

[tomtseng]

sad that this is necessary but i've run into this issue too

i suspect that in a few months time i'll forget what the _sb suffix means and why we bind and reassign variables like this... maybe std::tie is less confusing in that respect