Return data from [sync] SDAG methods
Once #870 is implemented, the next logical step is to make it possible to return values from SDAG code to callers. This may be possible to implement using just the declared return types of the methods in question, or it may be better using the C++14 feature
"Return type deduction for normal functions" described in standards committee paper N3638.
GCC implements this in versions 4.8 (N3386) and 4.9 (N3638). The feature test flag is
__cpp_decltype_auto >= 201304