Re: [boost] phoenix::bind

Subject: Re: [boost] phoenix::bind
From: Peter Dimov (pdimov_at_[hidden])
Date: 2008-09-30 07:35:17

Joel de Guzman:

> Alright, let's put it to a vote then. Here's my vote:
>
> Capture expressions by value:    +1
> Capture special objects by ref
> (e.g. cout, endl, arrays):       +1

This is not that different from Lambda, except that it has

Capture left side of = and @= by ref: +0.5

>> Const propagation is less of an issue in Phoenix because it has true 
>> local variables. With boost::bind and a suitably defined f, one can do
>>
>>    boost::bind( f, 0, 0, _1 )
>>
>> to approximate a lambda with two local variables, initially 0, and one 
>> argument.
>
> That's a nice trick! That can be quite useful on certain occasions.

If you manage to include both Phoenix and boost::bind, you can do a 
generator function that returns 1, 2, 3... with:

    boost::bind<int>( ++arg1, 0 )

Of course if you have Phoenix you should be able to do the same with

    lambda( _a = 0 )[ ++_a ]

but it doesn't seem to work. Maybe I'm doing something wrong. :-)

>> Phoenix doesn't need such tricks. But the question needs to be 
>> considered, and a balance has to be struck.
>
> What do you think would be a good balance?

I'm not sure yet. I like the const propagation feature of boost::bind, but I 
can't say how it'd work in the larger Phoenix context, and whether it 
wouldn't prove too error-prone for casual use.