Re: [Boost-users] [Phoenix] for_each calling push_back for stl containers

On 7/10/2012 6:21 AM, Jeffrey Lee Hellrung, Jr. wrote:

On Mon, Jul 9, 2012 at 3:07 PM, Ryan mailto:boost@qwerkle.com> wrote:

On Mon, Jul 9, 2012 at 2:57 PM, Nathan Ridge mailto:zeratul976@hotmail.com> wrote:

Actually that's not true. Without using Phoenix at all, just using Boost.Range, this is simply:

boost::push_back(string_tokens, tokens);

Interesting, I'll have to take a look at boost range.

As for your question about why Phoenix for_each requires a lambda, I'm afraid I don't understand Phoenix well enough to answer that. Perhaps Thomas can help us.

Lets hope he weighs in then. I would really like to understand this sticking point.

I'm pretty sure it's a scoping issue. Your inner and outer arg1's should actually bind at different times to different objects, and the only way to signify that is to use scope the inner arg1 in a phx::lambda construct.

[...] Yes, it's a scoping issue. Please read up: http://tinyurl.com/brufnnw In essence, anytime you need a higher-order function passed in as an argument (e.g. for_each's function argument), you'll need an explicit lambda. The for_each example is actually mentioned in the docs: http://tinyurl.com/cjy82f8 It's really not that bad as you characterized it. Explicit is always better than implicit. For example: for_each(arg1, lambda[cout << arg1]) This other example (again from the docs) *cannot* be done with an implicit (unscoped) syntax. Nor can this be done with the mechanisms in MPL or Boost.Lambda, for example: for_each(arg1, lambda(_a = arg2) [ push_back(arg1, _a) ] ) Only the de-Bruijn syntax can do this as well. Please read up before you bash the thing ;-) Regards, -- Joel de Guzman http://www.boostpro.com http://boost-spirit.com