What is your favorite D feature?

[Brad Anderson via Digitalmars-d]

On Thursday, 22 June 2017 at 00:48:25 UTC, Seb wrote:
> Hi,
>
> I am currently trying to modernize the D code example roulette 
> on the dlang.org front page [1]. Hence, I would love to hear 
> about your favorite feature(s) in D.
> Ideas:
> - favorite language construct
> - favorite code sample
> - "only possible in D"
>
> Before you ask, yes - I want to add a couple of cool examples 
> to dlang.org (and yep the roulette rotation is currently broken 
> [2]).
>
> [1] 
> https://github.com/dlang/dlang.org/pulls?q=is%3Apr+is%3Aopen+label%3A%22Frontpage+example%22
> [2] https://github.com/dlang/dlang.org/pull/1757

A very simple vibe app could be added using dub's single-file 
package format. Something like (I haven't tried this):

     #!/usr/bin/env dub
     /+ dub.sdl:
         name "hello"
         dependency "vibe-d" version="~>0.8.0-rc.1"
     +/
     import vibe.d;

     shared static this()
     {
         auto settings = new HTTPServerSettings;
         settings.port = 8080;

         listenHTTP(settings, &handleRequest);
     }

     void handleRequest(HTTPServerRequest req,
                   HTTPServerResponse res)
     {
         if (req.path == "/")
             res.writeBody("Hello, World!", "text/plain");
     }

     // Dependencies fetched, compiled, cached, built against, and 
result executed
     // in one command:
     //     $ ./hello.d