Ichthyostega
3614085ff7
This is a consequence of the experiments with generic lambdas. Up to now, lib::meta::_Fun<F> failed with a compilation error when passing the decltype of such a generic lambda. The new behaviour is to pick the empty specialisation (std::false_type) in such cases, allowing to guard explicit specialisations when no suitable functor type is passed
138 lines
4.5 KiB
C++
138 lines
4.5 KiB
C++
/* try.cpp - for trying out some language features....
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* scons will create the binary bin/try
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*
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*/
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// 8/07 - how to control NOBUG??
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// execute with NOBUG_LOG='ttt:TRACE' bin/try
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// 1/08 - working out a static initialisation problem for Visitor (Tag creation)
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// 1/08 - check 64bit longs
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// 4/08 - comparison operators on shared_ptr<Asset>
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// 4/08 - conversions on the value_type used for boost::any
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// 5/08 - how to guard a downcasting access, so it is compiled in only if the involved types are convertible
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// 7/08 - combining partial specialisation and subclasses
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// 10/8 - abusing the STL containers to hold noncopyable values
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// 6/09 - investigating how to build a mixin template providing an operator bool()
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// 12/9 - tracking down a strange "warning: type qualifiers ignored on function return type"
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// 1/10 - can we determine at compile time the presence of a certain function (for duck-typing)?
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// 4/10 - pretty printing STL containers with python enabled GDB?
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// 1/11 - exploring numeric limits
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// 1/11 - integer floor and wrap operation(s)
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// 1/11 - how to fetch the path of the own executable -- at least under Linux?
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// 10/11 - simple demo using a pointer and a struct
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// 11/11 - using the boost random number generator(s)
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// 12/11 - how to detect if string conversion is possible?
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// 1/12 - is partial application of member functions possible?
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// 5/14 - c++11 transition: detect empty function object
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// 7/14 - c++11 transition: std hash function vs. boost hash
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// 9/14 - variadic templates and perfect forwarding
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// 11/14 - pointer to member functions and name mangling
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// 8/15 - Segfault when loading into GDB (on Debian/Jessie 64bit
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// 8/15 - generalising the Variant::Visitor
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// 1/16 - generic to-string conversion for ostream
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// 1/16 - build tuple from runtime-typed variant container
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// 3/17 - generic function signature traits, including support for Lambdas
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// 9/17 - manipulate variadic templates to treat varargs in several chunks
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// 11/17 - metaprogramming to detect the presence of extension points
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// 11/17 - detect generic lambda
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/** @file try.cpp
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** Metaprogramming: is it possible to distinguish a generic lambda from something not a function at all?
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** Answer: not really. We can only ever check for the function call operator.
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** Even worse: if we instantiate a templated function call operator with unsuitable parameter types,
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** the compilation as such fails. Whereas SFINAE is only limited to substituting a type signature.
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*/
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typedef unsigned int uint;
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#include "lib/format-cout.hpp"
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#include "lib/format-util.hpp"
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#include "lib/meta/function.hpp"
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#include "lib/test/test-helper.hpp"
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//#include <functional>
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#include <utility>
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#include <string>
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using lib::meta::No_t;
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using lib::meta::Yes_t;
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using lib::meta::_Fun;
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using lib::test::showSizeof;
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using std::function;
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using std::forward;
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using std::move;
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using std::string;
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namespace lib {
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namespace meta{
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template<class FUN, typename...ARGS>
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struct ProbeFunctionInvocation
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{
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using Ret = decltype(std::declval<FUN>() (std::declval<ARGS>()...));
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using Args = Types<ARGS...>;
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using Sig = Ret(ARGS...);
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};
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}}
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using lib::meta::enable_if;
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#define SHOW_TYPE(_TY_) \
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cout << "typeof( " << STRINGIFY(_TY_) << " )= " << lib::meta::typeStr<_TY_>() <<endl;
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#define SHOW_EXPR(_XX_) \
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cout << "Probe " << STRINGIFY(_XX_) << " ? = " << _XX_ <<endl;
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long
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funny(int i)
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{
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return i+1;
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}
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template<typename FUN, typename SEL =void>
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struct FunTrait
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{
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using XXX = decltype(std::declval<FUN>() (0));
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static string doIt() { return "Uh OH:" + lib::meta::typeStr<XXX>(); }
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};
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template<typename FUN>
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struct FunTrait<FUN, enable_if<_Fun<FUN>> >
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{
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static string doIt() { return "Yeah FUN:" + lib::meta::typeStr<typename _Fun<FUN>::Sig>(); }
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};
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int
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main (int, char**)
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{
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auto lamb1 = [](int i) { return double(i) / (i*i); };
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auto lamb2 = [](auto i) { return double(i) / (i*i); };
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SHOW_TYPE (decltype(lamb1));
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SHOW_TYPE (decltype(lamb2));
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SHOW_EXPR ((_Fun<decltype(lamb1)>::value));
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SHOW_EXPR ((_Fun<decltype(lamb2)>::value));
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SHOW_EXPR ((_Fun<decltype(funny)>::value));
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SHOW_EXPR ((_Fun<decltype(&funny)>::value));
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auto funky = function<double(float)> (lamb2);
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SHOW_EXPR ((_Fun<decltype(funky)>::value));
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cout << FunTrait<decltype(lamb1)>::doIt() <<endl;
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cout << FunTrait<decltype(lamb2)>::doIt() <<endl;
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cout << FunTrait<decltype(funny)>::doIt() <<endl;
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cout << FunTrait<decltype(funky)>::doIt() <<endl;
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cout << "\n.gulp.\n";
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return 0;
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}
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