From: Peter Dimov (pdimov_at_[hidden])
Date: 2006-03-08 17:12:02
Scott Meyers wrote:
> Consider this (working) code using Boost.FileSystem:
>
> fs::directory_iterator di(dir);
> fs::directory_iterator end;
> while (di != end) {
> if (is_directory(*di)) cout << "D\n";
> else cout << "~D\n";
> ++di;
> }
>
> 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?
The cout << "D\n" subexpression is evaluated immediately since it doesn't
have any lambda components. Use var(cout) << "D\n" instead, or the ?:
variant:
cout << if_then_else_return( bind(&fs::is_directory, _1), "D\n",
"~D\n" )
You could also make an alias for var(std::cout):
var_type<std::ostream>::type cout = var( std::cout );
and use that in the lambda expressions.