Re: [Boost-users] [BGL] Bundled properties and property maps

Subject: Re: [Boost-users] [BGL] Bundled properties and property maps
From: Geoff Hilton (geoff.hilton_at_[hidden])
Date: 2009-01-26 15:49:56

Andrew Sutton wrote:
> 
>         val = get(pmap, k)
> 
>         So apparently, the concept definition actually requires that
>         property maps are never const - which is admittedly a little weird.
> 
> 
>     It sounds like we're now on the same page! The above essentially
>     means that it becomes literally impossible to write perfectly
>     const-correct code (from a user standpoint). While const-incorrect
>     code is bad enough, it also means that I may be missing out on
>     potential compiler optimizations, that bugs me quite a bit more.
> 
>     What may be done to remedy this?
> 
> 
> I will admit that writing perfectly const-correct code can be very, very 
> difficult in many situations :) However, I'll defer to more experienced 
> Boosters with regards that its impossible. I will also say that 
> const-incorrect code isn't necessarily "bad". There are times that 
> ignoring const-ness is quite useful.
> 
> In this particular instance, I will cautiously say that the concept 
> definition is implemented incorrectly. If the constraints() funciton did 
> this:
> 
> property_map<Key, Graph>::type pm = get(...);
> 
> instead of:
> 
> pm = get(),
> 
> It would preserve the const'ness of the pmap object, and the compiler 
> error might not exist.
> 
> I also wouldn't worry about compiler optimizations in this case. The 
> compiler is going to elide all or most of the pmap copies and inline all 
> off the function calls to the underlying data structures. Generally, 
> you'll never see the statement (pm = get(...)) in Boost.Graph algorithms.
> 
> Andrew Sutton
> andrew.n.sutton_at_[hidden]

Can this be fixed for 1.38?

Thanks,
Geoff