syntax for output parameters to function calls

[twicki]

cosunae: With C++-17 structured bindings feature,(supposedly available in clang 4) https://clang.llvm.org/cxx_status.html

we can improve the semantic of input/output in the function call

auto [u_tens_stage, v_tens_stage] = horizontal_advection::uv( u_stage, v_stage, tgrlatda0,
tgrlatda1);

[twicki]

thfabian: While I like this syntax, I think there are some open questions.

• Currently there is no way to deduce from the stencil definition if a storage is input, output or input-output. Meaning, one would need to inspect the code to deduce this information (the same problem exists also today but with the C function call syntax it is not a necessary information to provide). We would need some notation to distinguish between the cases. Something like:

  struct uv : public stencil {
  storage<in> u_stage, v_stage, tgrlatda0, tgrlatda1;
  storage<out> u_tens_stage, v_tens_stage;
  
  void Do() { ... }
  };

• Secondly, we need to discuss if we want to support multiple versions of Clang or we force one (e.g 4.0). I need to check how much efffort it is to upgrade from Clang 3.8 (which is currently in use) to 4.0.

[Stagno]

@twicki @cosunae Is this still useful?

[twicki]

so this is still possible - especially now that we've upgraded. I think we should keep it around if we feel like this would increase readability

[Stagno]

ok, still up then