template-based test function for unary operators?

[JanW]

Somewhat a C++ beginner, I'm trying to make a general test function
that could test unary operators (or methods) of an object of any class.

Arguments are a member-pointer to the function, a single input
argument of some type for that function, and the expected result of
some type. Then it tests if the result is as expected, and does some
logging of the results (pass, fail) etc.

Well, the template "mess" does not quite work out.

Below is the code. After that, the error messages.

--------------------------------------------------------

class A {
int f (int c) { return c; }
int f (const char c) { return c; }
A& operator+= (A const& a) { return *this; }
};

template <class rettype, class argtype, class btype>
bool unary_op_test(rettype (*func)(argtype),
btype self, argtype arg, rettype expect)
{
rettype rv = self.func(arg);
bool result = (rv == expect);
return result;
}

int main ()
{
A aa;
int (A::*p1)(int) = &A::f;
A& (A::*p2)(A const&) = &A:perator+=;
unary_op_test<int,int,A&>(p1, aa, 12, 12);
unary_op_test<A&,A&,A&>(p2, aa, aa, aa);
unary_op_test<A&,const A&,A&>(p2, aa, aa, aa);
}

--------------------------------------------------------

$ g++ -Wall -pedantic test.cc
test.cc: In function 'int main()':
test.cc:21: error: no matching function for call to
'unary_op_test(int (A::*&)(int), A&, int, int)'
test.cc:22: error: no matching function for call to
'unary_op_test(A& (A::*&)(const A&), A&, A&, A&)'
test.cc:23: error: no matching function for call to
'unary_op_test(A& (A::*&)(const A&), A&, A&, A&)'

--------------------------------------------------------

How come "A& (A::*&)(const A&)" does not map to "rettype
(*func)(argtype)"<templated> i.e. to "A&(*func)(const A&)"?

Sure some beginner mistake somewhere...

Any ideas?

- Jan

 

[JanW]

JanW wrote:

Only one idea so far: the type "a pointer to a [non-static] member
function of class T" is not convertible to "a pointer to function".

Oops, true. That was quick, thanks

After the first attempts it has now started working. As a first
version, just rewriting unary_op_test() to like below (and defining
A:perator== in class A) removes the complaints:

template <class rettype, class argtype, class btype>
bool unary_op_test(rettype (btype::* func)(argtype), btype& self,
argtype arg, rettype expect)
{
rettype rv = (self.*func)(arg);
bool result = (rv == expect);
return result;
}

And then call the tests like below:

unary_op_test<int,int,A>(p1, aa, 12, 12);
unary_op_test<A&,const A&,A>(p2, aa, aa, aa);
unary_op_test(p1, aa, 12, 12);

Thanks!

- Jan

 

[Gennaro Prota]

Well, the template "mess" does not quite work out.

Below is the code. After that, the error messages.

--------------------------------------------------------

class A {
int f (int c) { return c; }
int f (const char c) { return c; }
A& operator+= (A const& a) { return *this; }
};

template <class rettype, class argtype, class btype>
bool unary_op_test(rettype (*func)(argtype),
btype self, argtype arg, rettype expect)
{
rettype rv = self.func(arg);
bool result = (rv == expect);
return result;
}

int main ()
{
A aa;
int (A::*p1)(int) = &A::f;
A& (A::*p2)(A const&) = &A:perator+=;
unary_op_test<int,int,A&>(p1, aa, 12, 12);
unary_op_test<A&,A&,A&>(p2, aa, aa, aa);
unary_op_test<A&,const A&,A&>(p2, aa, aa, aa);
}

Pointers to member functions are not pointers to functions, and there's
no implicit conversion. There are other issues in your code, but this is
the main one. Here's a rough function template accepting a pointer to
member function:

template< typename Ret, typename C, typename Arg>
void f( Ret ( C::*pmf )( Arg ),
C & c,
Arg a )
{
( c.*pmf )( a ) ;
}

usable as follows:

A instance = {} ;
int ( A::*p1 )( int ) = &A::f;
f( p1, instance, 12 ) ;