phobos dependencies

[H. S. Teoh]

On Fri, Dec 20, 2013 at 09:27:55AM -0800, Andrei Alexandrescu wrote:
> On 12/20/13 5:45 AM, Joseph Rushton Wakeling wrote:
> >On 20/12/13 10:06, Meta wrote:
> >     void topN(alias less = "a < b",
> >             SwapStrategy ss = SwapStrategy.unstable,
> >             Range, RandomGen)(Range r, size_t nth, ref RandomGen rng)
> >         if (isRandomAccessRange!(Range) && hasLength!Range
> >             && isUniformRNG!RandomGen)  // <--- needs
> >std.random.isUniformRNG
> >     {
> >         static assert(ss == SwapStrategy.unstable,
> >                 "Stable topN not yet implemented");
> >         while (r.length > nth)
> >         {
> >             auto pivot = uniform(0, r.length, rng);
> >             // ... etc. ...
> >         }
> >     }
> 
> I had this idea fot a while, and Walter is favorable of it as well -
> extend "import" for one-shot use. With that feature the example
> would become:
> 
>     void topN(alias less = "a < b",
>             SwapStrategy ss = SwapStrategy.unstable,
>             Range, RandomGen)(Range r, size_t nth, ref RandomGen rng)
>         if (isRandomAccessRange!(Range) && hasLength!Range
>             && import.std.random.isUniformRNG!RandomGen)
>     { ... }
> 
> In this case "import" would syntactically be placed at the beginning
> of a qualified name, meaning "import this module lazily and look up
> the symbol in it".
[...]

Hmm. Why do we need to incorporate the 'import' keyword in the first
place? 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) ...

and the compiler will automatically import std.range within that scope.
Obviously, it's a bad idea to import std.range into module scope, since
it would pollute the module namespace, but it seems a good idea to do a
one-shot import automatically, since the qualified symbol itself already
says which module the symbol is supposed to be defined in. There's no
need to add another "import." prefix to it, IMO.


T

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