Re: [Boost-users] [Lambda] Help with if_then_else

From: Daniel James (daniel_james_at_[hidden])
Date: 2006-03-08 17:08:28

On 3/8/06, Scott Meyers <usenet_at_[hidden]> wrote:
> This looks like it should be lambda-able.  Here's my attempt:
>
>    for_each(fs::directory_iterator(dir), fs::directory_iterator(),
>             if_then_else(bind(&fs::is_directory, _1),
>                          cout << "D\n",
>                          cout << "~D\n"));
>
> VC7.1 doesn't like this -- the diagnostics are below.  Any idea how I can make
> this work?

Try out:

    for_each(fs::directory_iterator(dir), fs::directory_iterator(),
             if_then_else(bind(&fs::is_directory, _1),
                          cout << constant("D\n"),
                          cout << constant("~D\n")));

The problem is that 'cout << "D\n"' is getting called immediately - as
it's not a lambda expression, by making "D\n" a delayed constant it
becomes one. This is documented at http://tinyurl.com/7jq3v.

Hope that helps,

Daniel