#12 Functor operator ==

[Eric Beyeler]

Functor needs an operator ==. This is not a hard
implementation, as I have made this modification in
our code. Boost::function has this as well. See my
posts in the general forum.

[Peter Kuemmel]

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Is it possible to submit your already tested implementation?
That would be great.
I could test it with vc8.

[Peter Kuemmel]

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Here a first attempt inspired by Eric.
But a full implementation is much more work.
It also shows some problems with the design of Functor.
it only works with msvc and breaks Function as drop in for
boost::function.

Index: Functor.h

RCS file: /cvsroot/loki-lib/loki/include/loki/Functor.h,v
retrieving revision 1.18
diff -u -B -b -r1.18 Functor.h
--- Functor.h 27 Feb 2006 18:53:41 -0000 1.18
+++ Functor.h 7 Mar 2006 10:34:07 -0000
@@ -42,6 +42,8 @@
//#define LOKI_FUNCTOR_IS_NOT_A_SMALLOBJECT
#endif

+#define LOKI_ENABLE_FUNCTOR_EQUAL
+
namespace Loki
{
////////////////////////////////////////////////////////////////////////////////
@@ -95,6 +97,13 @@
assert(typeid(*pClone) == typeid(*pObj));
return pClone;
}
+
+#ifdef LOKI_ENABLE_FUNCTOR_EQUAL
+ virtual bool operator==(const FunctorImplBase&) const = 0;
+ // there is no static information if Functor holds a
member function
+ virtual bool isMemberFuncPtr() const = 0;
+#endif
+
};
}

@@ -942,6 +951,18 @@

LOKI_DEFINE_CLONE_FUNCTORIMPL(FunctorHandler)

+#ifdef LOKI_ENABLE_FUNCTOR_EQUAL
+ bool isMemberFuncPtr() const
+ { return false; }
+
+ bool operator==(const typename Base::FunctorImplBase&
rhs) const
+ {
+ if( rhs.isMemberFuncPtr() )
+ return false; // cannot be equal
+ const FunctorHandler& fh = static_cast<const
FunctorHandler&>(rhs);
+ return f_==fh.f_;
+ }
+#endif
// operator() implementations for up to 15 arguments

ResultType operator()()
@@ -1051,6 +1072,18 @@

LOKI_DEFINE_CLONE_FUNCTORIMPL(MemFunHandler)

+#ifdef LOKI_ENABLE_FUNCTOR_EQUAL
+ bool isMemberFuncPtr() const
+ { return true; }
+
+ bool operator==(const typename Base::FunctorImplBase&
rhs) const
+ {
+ if( !isMemberFuncPtr() )
+ return false;
+ const MemFunHandler& mfh = static_cast<const
MemFunHandler&>(rhs);
+ return pObj_==mfh.pObj_ && pMemFn_==mfh.pMemFn_;
+ }
+#endif
ResultType operator()()
{ return ((*pObj_).*pMemFn_)(); }

@@ -1223,6 +1256,18 @@
return *this;
}

+#ifdef LOKI_ENABLE_FUNCTOR_EQUAL
+ bool operator==(const Functor& rhs) const
+ {
+ return *spImpl_.get() == *rhs.spImpl_.get();
+ }
+
+ bool operator!=(const Functor& rhs) const
+ {
+ return !(*this==rhs);
+ }
+#endif
+

[Peter Kuemmel]

small test program

[Peter Kuemmel]

with minimalistic operator==

[Peter Kuemmel]

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Relates stuff:

http://www.codeproject.com/cpp/FastDelegate.asp

Herb Sutter:
http://www.ddj.com/dept/cpp/184403873
Generalizing the Observer pattern (essentially, multicast
delegates) using std::tr1::function. Discusses the
limitations of the failure of boost::function to provide
operator ==.