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Investigation: failure to detect nested typedef

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a metafunction to detect nested typedefs worked perfectly in the test setup,
but failed once included into application code.
This commit is contained in:
Fischlurch 2017-11-30 23:58:57 +01:00
parent b104508685
commit 2c53dc2e57
1 changed files with 11 additions and 68 deletions
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79
research/try.cpp
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@ -35,52 +35,29 @@
// 9/17 - manipulate variadic templates to treat varargs in several chunks
// 11/17 - metaprogramming to detect the presence of extension points
// 11/17 - detect generic lambda
// 12/17 - investigate SFINAE failure
/** @file try.cpp
** Metaprogramming: is it possible to distinguish a generic lambda from something not a function at all?
** Answer: not really. We can only ever check for the function call operator.
** Even worse: if we instantiate a templated function call operator with unsuitable parameter types,
** the compilation as such fails. Whereas SFINAE is only limited to substituting a type signature.
** Bug hunting: a typedef detecting metafunction fails under circumstances yet to be investigated.
*/
typedef unsigned int uint;
#include "lib/meta/value-type-binding.hpp"
#include "lib/diff/gen-node.hpp"
#include "lib/format-cout.hpp"
#include "lib/format-util.hpp"
#include "lib/meta/function.hpp"
#include "lib/test/test-helper.hpp"
//#include <functional>
#include <utility>
#include <string>
using lib::meta::No_t;
using lib::meta::Yes_t;
using lib::meta::_Fun;
using lib::test::showSizeof;
using std::function;
using std::forward;
using std::move;
using std::string;
namespace lib {
namespace meta{
template<class FUN, typename...ARGS>
struct ProbeFunctionInvocation
{
using Ret = decltype(std::declval<FUN>() (std::declval<ARGS>()...));
using Args = Types<ARGS...>;
using Sig = Ret(ARGS...);
};
}}
using lib::meta::enable_if;
//using lib::meta::enable_if;
using ElmIter = lib::diff::RecordSetup<lib::diff::GenNode>::ElmIter;
using RecIter = lib::diff::Rec::iterator;
#define SHOW_TYPE(_TY_) \
@ -89,48 +66,14 @@ using lib::meta::enable_if;
cout << "Probe " << STRINGIFY(_XX_) << " ? = " << _XX_ <<endl;
long
funny(int i)
{
return i+1;
}
template<typename FUN, typename SEL =void>
struct FunTrait
{
using XXX = decltype(std::declval<FUN>() (0));
static string doIt() { return "Uh OH:" + lib::meta::typeStr<XXX>(); }
};
template<typename FUN>
struct FunTrait<FUN, enable_if<_Fun<FUN>> >
{
static string doIt() { return "Yeah FUN:" + lib::meta::typeStr<typename _Fun<FUN>::Sig>(); }
};
int
main (int, char**)
{
auto lamb1 = [](int i) { return double(i) / (i*i); };
auto lamb2 = [](auto i) { return double(i) / (i*i); };
SHOW_TYPE (ElmIter);
SHOW_TYPE (RecIter);
SHOW_TYPE (decltype(lamb1));
SHOW_TYPE (decltype(lamb2));
SHOW_EXPR ((_Fun<decltype(lamb1)>::value));
SHOW_EXPR ((_Fun<decltype(lamb2)>::value));
SHOW_EXPR ((_Fun<decltype(funny)>::value));
SHOW_EXPR ((_Fun<decltype(&funny)>::value));
auto funky = function<double(float)> (lamb2);
SHOW_EXPR ((_Fun<decltype(funky)>::value));
cout << FunTrait<decltype(lamb1)>::doIt() <<endl;
cout << FunTrait<decltype(lamb2)>::doIt() <<endl;
cout << FunTrait<decltype(funny)>::doIt() <<endl;
cout << FunTrait<decltype(funky)>::doIt() <<endl;
SHOW_TYPE (lib::meta::TypeBinding<ElmIter>::pointer);
cout << "\n.gulp.\n";