Re: [Cppunit-devel] equality of const objects

[Duane M. <dua...@ma...>]

--- At Mon, 1 Oct 2001 16:32:52 -0400, Steve M. Robbins wrote:

>On Mon, Oct 01, 2001 at 12:45:40PM -0700, Duane Murphy wrote:
>
>> I would also make the argument (FWIW) that const is all that is needed.
>> Comparison operators should not be mutating. (Caches are caches and
>> should be marked mutable.)
>
>I happen to agree with you.  If it were my decision alone, I'd just
>leave things as-is and let the folks who can't compare const objects
>to suffer for their sins.  ;-)

In discussing this with our group, we will be removing the non-const
features from our version of the library. We feel that it is important to
enforce const equality tests. C++ gives us lots of power to do strange
and unusual things. We need all the help we can get to make sure we are
doing the right thing.

>> This is also where you want to make the change for comparing equivalent
>> objects (not the same type). The change would be thus:
>> 
>>      template <class TExepect, TActual>
>>      void assertEquals( const TExepect & expected,
>>                         const TActual & actual, ... )
>
>I'm fairly skeptical that we want to allow this.  
>
>I seem to recall changing my local copy of CppUnit some months ago to
>allow assertEquals() on two different types.  And I seem to recall
>running into problems because the compiler likes to promote types
>and use implicit conversions and all the other good stuff.  
>Sorry to not be more specific at this point...

You are of course correct. This is one of the places that concerns me
most in writing C++. Those conversions can magically make code do very
unexpected things.

>The question, in my mind, is: why are you comparing two different
>types for equality, anyway???
>
>There are two alternatives that come to mind:
>
>1. Construct an appropriate "expected" value to begin with.
>   If you claim the two types are "equivalent", then you should
>   be able to construct an appropriate object.  In the enum/int
>   example, use CPPUNIT_ASSERT_EQUAL( int(noErr), FunctionToTest() );

This turns out to be the best suggestion for my simple example.

>2. Make up your own comparison functions and use CPPUNIT_ASSERT.
>
>	bool my_equality_T1_T2( const T1& x, const T2& y ) { ... }
>
>	#define CPPUNIT_ASSERT_EQUALS_T1_T2(x,y) \
>		CPPUNIT_ASSERT( my_equality_T1_T2(x,y) )
>
>   I do this sort of thing all the time.  Not everything needs to be 
>   in the base library.

Thanks, this is a good suggestion!