Why not app.use(generator) ?

[azproduction]

Like this

app.use(function *(next) {
    var start = new Date;
    yield next;
    var ms = new Date - start;
    console.log('%s %s - %s', this.method, this.url, ms);
});

Is there a reason for that?

[tj]

just because of how we're composing them it basically passes next to all of them first and becomes:

b(c(d(e(f(notfound)))))

I had thought about doing what you mention but it would require that we use a dispatcher

[jonathanong]

+1. i find nesting another function pretty annoying, especially when we're trying to avoid callbacks.

[tj]

dispatchers are not great though, and become a reasonable source of slow down when you start mounting a lot of apps, which is one thing I'd like to get "right" with koa. With Connect the dispatcher adds considerable overhead when you have a decent size tree of apps, and it makes composition a lot more difficult / coupled to koa, but I'll see if I can find a decent way around that. If ES6 would allow yield; as yield undefined; we could just have yield and that's it. I'll try this out again and see what impact it has, it also means we can't use co due to how it's designed

[jonathanong]

Errrr yeah I just realized how complicated it would make things. Personally, I wouldn't mind performance penalties as long as they aren't crippling. We can always improve the dispatcher (or try to) but changing the middleware signature would be difficult.

[tj]

having an intermediate is helpful for debugging though, you can print out the currently executing middleware and mutations made etc, so it might be worth the added complexity, I'll see if I can refactor koa-compose to not be disgusting haha and hopefully the accumulated perf portion is not too bad with lots of mounting, we'll find out!

I have it working with the following, but mounting would definitely be much more complex than it is now:

app.use(function *(){
  console.log('before')
  yield 'next';
  console.log('after')
})

[jonathanong]

how about just allowing any "falsey" value instead of 'next'?

var next;

app.use(function *(){
  console.log('before');
  yield next;
  console.log('after');
})

meh it doesn't really matter. being able to just do yield 0 would be nice though.

[tj]

yeah fuck it, way too awkward for mounting, we can maybe revisit this in the future, it does look nicer but implementation obscurity is probably not worth it. Closing for now

[jonathanong]

You got the code on a branch? I want to check it out.

[tj]

@jonathanong https://github.com/koajs/koa/tree/add/dispatcher

just enough to get examples/simple.js working

[tj]

another nice thing about the dispatcher approach though is we can remove downstream, since we can check that it's reached the furthest downstream middleware

[tj]

maybe we'll see it changed: