Re: [boost] Case study: Boost.Local versus Boost.Phoenix

Subject: Re: [boost] Case study: Boost.Local versus Boost.Phoenix
From: Simonson, Lucanus J (lucanus.j.simonson_at_[hidden])
Date: 2011-02-07 13:44:06

Phil Endecott wrote:
> Simonson, Lucanus J wrote:
>> 
>> Phil Endecott wrote:
>>> The main complaint about that from the advocates of both Pheonix and
>>> Local seems to be that it's too far from the point of use.
> 
>> It isn't a matter of distance or familiarity, it is a matter of
>> scope. 
> 
> Right, typically you have to pass-by-reference any local variables
> that 
> you need to the functors' constructor.  It would often be better to
> have automatic access to the content of the local scope.  C++0x
> lambdas 
> can have that.
> 
> With Boost.Local I believe that you still have to explicitly capture
> the local variables that you need: (approximate syntax here:)
> 
> void my_function()
> {
>      foo_type foo;
>      bar_type bar;
> 
>      BOOST_LOCAL_FUNCTION(
>      (void) (my_lambda) ( (arg_type)(a) (bind)(&foo) (bind)(&bar) )
>      ) { .......
> 
> Note the (bind)(&foo) bit.
> 
>> If we instead declare the function as a local function it has
>> access to the local scope data of the function in which it was
>> declared 
> 
> If Boost.Local has some way to automatically access variables in the
> scope in which it is declared without having to explicitly list them,
> that is something that I have missed.

I never looked at the library.  I didn't plan on using it or participating in the review and I'm not sure what problem it is solving with these macros.  I was talking about local functions in general.  What is wrong with:

void my_function()
{
     foo_type foo;
     bar_type bar;

     void my_lambda( arg_type a)
     { .......

Is it that my_lambda isn't allowed to be a template parameter or some other strange restriction on local functions or local functions aren't allowed in template functions?  I know there was a linker problem with local functions in header files, which sort of interferes with their use in templates.

If the library doesn't allow access to a local variable without passing them to a macro what's the point?  I can easily declare a struct with members that reference the local varaibles and construct one then pass it as a functor.  Did this guy just do that and wrap it with a macro?

Regards,
Luke