Re: [boost] Re: Callbacks Again

From: Jesse Jones (jesjones_at_[hidden])
Date: 2000-11-18 17:11:10

>--- In boost_at_[hidden], Jesse Jones <jejones_at_a...> wrote:
>> >On Fri, 17 Nov 2000 15:31:35 -0800
>> >Jesse Jones <jejones_at_a...> wrote:
>> But we know that we want to have some sort of empty test. If we do 
>this
>> with a bool or const void* conversion operator users will be able to
>> compare any two callback objects, but in all probability this will 
>return
>> false unless you're dealing with the exact same callback on the 
>left and
>> right.
>
>Actually, with the conversions in place comparisons will usually 
>return true.  cb1 converts to a bool (likely true) and cb2 converts 
>to a bool (likely true) and hence comparison likely returns true 
>regardless if the callbacks are exactly the same.  

For bool conversions any two non-empty callback objects will compare 
equal. For const void* conversions they'll compare not equal.

>(Actually, I'm 
>quite tired while writing this and I'm not sure that the implicit 
>conversions should occur in this case.  I'm fairly sure that if the 
>callbacks are of the same type the conversion will not occur.)

Why?

>> We can document that comparisons don't work as expected, but it
>> seems better to arrange for a compile error if the user does 
>something
>> wrong.
>
>That's simple.  You eliminate the comparison operations from the 
>public interface (explicitly make them private).  It's then a 
>compiler error to try and use them, which is the best idea 
>considering we can't make them return useful information.

Yeah, but since they're not one of the magic methods synthesized by the 
compiler I don't see why we need to declare them at all.

  -- Jesse