This question relates to an earlier one I asked regarding implementing something akin to Qt's signal/slots in C++11.
Consider the following (very simplified signal dispatcher, that in this example does nothing of any use, it's just to demonstrate the pattern/problem):
template< typename... TYPES >
class Signal
{
public:
Signal() = default;
~Signal() = default;
template< typename... PARAMETERS >
void broadcast( PARAMETERS &&... p )
{
// static_assert to confirm PARAMETERS can map to TYPES
}
};
This works well enough, but there's some unwanted type conversion going on in practice. e.g.;
// acceptable use.
Signal< int, unsigned, float, char >().broadcast( 1, 2u, 0.f, 'a' );
// should fail compilation, first parameter is a float, 4th is an int.
Signal< int, unsigned, float, char >().broadcast( 0.f, 0, 0.f, 0 );
// acceptable use, first parameter is const, but it's convertible.
const int i = 3;
Signal< int, unsigned, float, char >().broadcast( i, 2u, 0.f, 'a');
// acceptable use, first parameter is const &, but it's convertible.
const int & j = i;
Signal< int, unsigned, float, char >().broadcast( j, 2u, 0.f, 'a');
There should be no silent float to int conversion. Conversion of const/const & in this instance should be possible (the format of TYPES should not have const or & as all data should be passed by value).
I'd like to prevent compilation where such unwanted type conversion happens. I thought to wrap up both TYPES and PARAMETERS in tuples, iterate over the tuple and confirm that each type in a given tuple parameter index matches (including using std::decay
), but then I couldn't see a way to do that at compile time so that it could go in a static_assert
.
For reference, compilers of choice are clang (latest on OS X 7.3 (clang-703.0.31)) and vc14.
Is what I want to do possible and, if so, can anyone offer any pointers?
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