DIP10005: Dependency-Carrying Declarations is now available for community feedback

[Andrei Alexandrescu via Digitalmars-d]

On 12/14/2016 02:22 PM, Timothee Cour via Digitalmars-d wrote:
> What about simply this:
>
>
> ```
> module foo;
>
> {
> import std.stdio;
> void fun(File foo){}
> }
>
> {
> import sd.range;
> void foo(T) if(isInputRange!T){}
> }
>
> ```

Walter proposed this as well. We found two problems with it: (a) it is 
not clear that the import is effected only if the name is looked up; (b) 
the common case is one import clause for one declaration, which makes 
the code awkward. Either you have an indirection level to start with:

{
     import std.range;
     void foo(T) if(isInputRange!T)
     {
         ... one extra indent already ...
     }
}

or the horror of C++ namespaces:

{import std.range;

void foo(T) if(isInputRange!T)
{
    ...
}
}

The fact that C++ namespaces introduce scopes has been an unpleasant 
mistake. Virtually all coding standards I've seen make 
namespace-introduced scopes special in that they don't participate in 
the usual indentation rules. Even special emacs and vi rules have been 
devised for that. Something we can learn from.


Andrei