lazy import, an alternative to DIP 1005

[Jonathan Marler via Digitalmars-d]

On Friday, 15 September 2017 at 14:45:01 UTC, Jonathan Marler 
wrote:
> ...

Wanted to add that I believe we could also make "selective 
imports" lazy, either be default or possibly by adding a modifier 
like "lazy" if non-lazy imports are still useful.

lazy import std.stdio : File;
lazy import std.range : isInputRange;

void process(File input) ;
struct Buffered(Range) if (isInputRange!Range)
{
     ...
}

It works because the semantic analyzer knows that the "File" 
symbol is referring to something in module std.stdio, so it can 
delay importing std.stdio until it needs to resolve the File 
symbol.

If this was implemented, not sure if there is a benefit to 
turning lazy imports on/off, if not, then we could just forgo the 
new "lazy" modifier and just make all "qualified imports" lazy.

Note this can't work with normal imports because in that case you 
need to import the module just to know what symbols it contains.  
This idea only works with "static imports" and "selective 
imports".