Re: [boost] [Graph][Property map] Why aren't property maps function objects?

From: Ronald Garcia (garcia_at_[hidden])
Date: 2003-12-06 14:59:56

Douglas Gregor wrote:

>On Saturday 06 December 2003 11:32 am, garcia wrote:
>  
>
>>Douglas Gregor wrote:
>>    
>>
>>>
>>>Would anyone object if I made property maps into function objects? Any
>>>downsides?
>>>      
>>>
>>Are you suggesting changing the interface specified by the concepts in
>>the property map library, specifically, the LValuePropertyMap?
>>    
>>
>
>Yep. Essentially adding pmap(key) as a synonym for pmap[key]. Granted, I'd 
>like pmap(key) to return an lvalue for an lvalue property map, a 
>convertible-to-T for a readable property map, and an assignable-from-T from a 
>writable property map, just so it can be consistently used.
>
>  
>
Got it.  I don't think that's a good idea.  My reasoning is this:  The 
property-map interface allows for a great deal of flexibility in the 
implementation of property maps.  That is, a model of the Readable (or 
Writeable) Property Map concepts need not provide any member functions.

This is important especially when adapting a non-BGL graph type to
use BGL algorithms (take it from one who's been there ;) ).  Under those 
circumstances, it is very *good* to be able to construct a property map 
interface by simply adding traits classes and overloads of put() and/or 
get().

I guess I could almost see adding operator() to LValuePropertyMap, but 
then the property-map-as-function-object idiom would only work for that 
special case of property map. 

So, given these issues, I think that it would be better to provide a 
means to easily wrap property maps into a function objects. 

Cheers,

ron