Ichthyostega
a205653cad
Conversion means automatic conversion. In our case, what we need ist the ability to *construct* a bool from our (function) object -- while functors aren't automatically convertible to bool. Thus we use one of the new predicates from <type_traits>
80 lines
2.8 KiB
C++
80 lines
2.8 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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/** @file try.cpp
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** Investigation: empty and unbound function objects.
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** Since \c std::function is bool convertible, it should be possible to detect an empty or
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** unbound functor object and record this state in a VTable. Actually this approach used to
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** work with tr1::function objects. But it ceased to work after switching to c++11
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**
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** The reason is the more concise meaning of \em convertibility with C++11 -- now, an
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** automatic conversion is required; thus what we need is rather the ability to \em construct
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** our target type from the given source explicitly, which is a weaker requirement.
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**
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*/
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#include <type_traits>
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#include <functional>
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#include <iostream>
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//using std::placeholders::_1;
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//using std::placeholders::_2;
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using std::function;
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using std::bind;
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using std::string;
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using std::cout;
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using std::endl;
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uint
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funny (char c)
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{
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return c;
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}
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using FUC = function<uint(char)>;
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int
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main (int, char**)
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{
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FUC fun(funny);
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FUC empty;
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cout << "ASCII 'A' = " << fun('A');
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cout << " defined: " << bool(fun)
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<< " undefd; " << bool(empty)
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<< " bool-convertible: " << std::is_convertible<FUC, bool>::value
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<< " can build bool: " << std::is_constructible<bool,FUC>::value
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<< " bool from string: " << std::is_constructible<bool,string>::value;
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cout << "\n.gulp.\n";
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return 0;
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}
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