New guideline to place import statements as locally as possible

[Steve Teale]

On Friday, 21 March 2014 at 08:05:09 UTC, monarch_dodra wrote:
> On Friday, 21 March 2014 at 07:24:43 UTC, Steve Teale wrote:
>> Can someone tell me where this is written up?
>>
>> Thanks
>> Steve
>
> You mean generally, or in phobos?
>
> The rational in phobos is that since it is heavily templated, 
> it makes sense to pull the imports on a "as needed" basis.
>
> If we placed all the imports needed *anywhere* in the module at 
> the top, in *all* modules, then importing *anything* in std 
> would import the world.
>
> for example, something as "dumb" as TypeTuple:
>
> => need std.typetuple
> => pulls traits
> => pulls typecons and algorithm
> => pulls array, string, uni, ascii, utf, conv
> => pulls everything remaining
>
> The new scheme allows massively reducing these dependencies. At 
> least, that's the point. cross-module aliasing, and template 
> constraints tend to make this as smooth as we'd like it.
>
> In end user code, or in non-template code, there is less 
> rational for doing this. At that point, it only becomes a 
> style, issue, of whether or not you want to "pollute" your 
> namespace with imported symbols.

OK, so what happens that's different when I pull in std.typetuple 
at the point where I need it? Does that avoid pulling in all the 
other stuff?

How does this problem manifest itself - code bloat, or slower 
compilations, or what?

Thanks
Steve