From: Beman Dawes (bdawes_at_[hidden])
Date: 2003-08-22 15:06:40
At 11:35 PM 8/21/2003, David Abrahams wrote:
>Beman Dawes <bdawes_at_[hidden]> writes:
>
>> At 06:38 PM 8/21/2003, David Abrahams wrote:
>>
>> >I need to make a mapping over paths. Is there any important reason
>> >there's no operator< provided?
>>
>> I don't think it has been discussed. I've had the need myself, but
>> worked around it by using path::string() to generate the key.
>>
>> There were a number of discussions about operator== and !=. They can
>> be subject to serious abuse and misunderstanding, and so are left
>> out.
>
>Whoa, really?
>
>> I'm still not sure if that was the right decision, so might be
>> willing to review it.
>
>I'm curious about it, anyway.
Is path("abc")==path("ABC") true in the sense of being the same path? The
correct answer is yes, no, or maybe, depending on the operating system.
There are a ton of other examples where two paths which are textually
different are sometimes the same path.
The counter argument is that defining path equality as path::string()
equality seems natural, even if it doesn't answer the "are they the same
path?" question. But this does lead to fragile programs; we can see that in
the Boost regression test reporting where slight changes in the way bjam
reports paths often break the status tables (which rely on assumptions
about path equality.) operator== on paths can be a sign of poor, or at
least fragile design.
--Beman
PS: I just changed the FAQ entry to use that example; it is clearer than
the one given before.