phobos dependencies

[monarch_dodra]

On Friday, 20 December 2013 at 17:57:46 UTC, Andrei Alexandrescu 
wrote:
> On 12/20/13 9:38 AM, H. S. Teoh wrote:
>> What about extending symbol lookup, so that if a 
>> fully-qualified
>> symbol x.y.z can't be found in the current symbol tables, and 
>> x/y exists
>> in the current import path, then implicitly try to import x.y 
>> and lookup
>> z in that module. Then you could just write:
>>
>> 	void f(T)(T t) if (std.range.isInputRange!T) ...
>
> Due to a bug that's actually the case today to some extent :o).
>
>
> Andrei

In regards to template restraints, it *would* be kind of nice to 
be able to trigger import only when overload resolution begins.

For example, just because a function requires 
"std.range.isInputRange" to validate its inputs/overloads, 
doesn't mean it *has* to be globally imported into the entire 
module.

In this sense, it would be nice to be able to define an "import" 
block for such a function:
//----
module wow;

void bar(T)(T t)
if (isInputRange!T)
import
{
     std.range;
}
body
{
     ....
}

void foo()
{
     ....
}

//----

With such an approach, "std.range" only gets imported if a call 
is "attempted" to bar. if no such call is even attempted, then 
range isn't imported at all.

In this example, "foo" simply does not know about range. It is 
scoped to bar.

As a client, *if* I make no calls to bar, then I will not trigger 
a dependency to range in wow at all.