DIP11: Automatic downloading of libraries

[Andrei Alexandrescu]

On 6/14/11 10:26 AM, Daniel Gibson wrote:
> One additional file. I don't think having one file would be a burden to
> the programmer, not much more than adding pragmas in his code.
>
> But if there's central metadata repository even this additional file
> isn't needed - neither are pragmas - (the build-tool will ask that repo
> where to find the lib/module), unless the lib is kind of obscure or
> brand-new and thus not known by the metadata repo. And in that case:
> it's just a single file.
>
> (Of course it would be possible to periodically or via "build-tool
> update" - like apt-get update - fetch the metadata, so the server
> doesn't have to be asked each time.)

I agree that a build tool is an alternative. The problem is that it's 
front-heavy - we need to design the config file format, design the tool 
to deal with various dependency issues etc. Many of these issues are 
solved by design or don't even exist with the pragma, for example 
there's no need for a config file format or for config files in the 
first place (although they can be easily defined as small .d files 
consisting of pragmas).

One thing I like about the pragma is that it's mostly mechanism and very 
little policy, while at the same time fostering very simple, 
straightforward policies. Source files can carry their own dependencies 
(but they don't need to), transitivity just works, (re|in)direction and 
central repos are possible without being required.

One other interesting aspect is that the string literal can be 
CTFE-constructed, i.e. may include a path to a library depending on the 
OS, version, etc. An external tool would need to give up on that (and 
use multiple configuration files) or invent its own string manipulation 
primitives.


Andrei