Re: [Boost-users] Equality comparison of boost::function<>

Subject: Re: [Boost-users] Equality comparison of boost::function<>
From: Steven Watanabe (watanabesj_at_[hidden])
Date: 2009-08-10 14:17:56

AMDG

Zachary Turner wrote:
> On Mon, Aug 10, 2009 at 10:51 AM, Steven Watanabe<watanabesj_at_[hidden]> wrote:
>   
>> This ought to return false because the types are different.
>>
>>     
>>> So in short, what is the flaw in just testing the way two function
>>> objects are represented internally
>>>       
>> It would be surprising, because nothing else works that way.
>>     
>
> I agree it might be surprising from an implementation standpoint.  But
> are there examples of functors such that equality implemented this way
> would return a surprising result?

boost::lambda::_1 == std::string()

The result of memcmp depends on the implementation details of
std::string.

> If the result isn't surprising,
> then I don't think the implementation should matter much, as long as
> it relies only on standards conformant language aspects.
>   

memcmp is not guaranteed to produce sensible results in this
context.  I don't know that it is even guaranteed to work for
POD types, when padding is added for alignment reasons.

> Again I could just be overlooking something due to lack of
> understanding of the implementation details of boost::function<>, but
> at least on the surface it seems to me that the behavior would always
> produce expected results

In Christ,
Steven Watanabe