Trying to reproduce Node.js async waterfall pattern.. (Meta-programming)

[Philippe Sigaud via Digitalmars-d-learn]

> Yes, the final callback is always called, but if an error is passed to the
> callback by any of the main steps in the "sequence ladder", it will
> immediately jump to the final callback and not execute further steps.

OK.


>> What do you mean? The compiler does deduce the type of Funcs.
>
>
> If you look at where I call Waterfall() in main, you'll see I had to
> manually specify (Callback cb) instead of just (cb); since it didn't know
> that the Funcs... were of type AsyncFunc

you can use std.typetuple.allSatisfy with a helper template:

enum isAsyncFunc(T) = is(T == AsyncFunc);

... (Funcs...)(Funcs funcs) if (allSatisfy!(isAsyncFunc, Funcs))
{ ... }



>> (cb) { cb(null, "one");} is possible, but that means it's a function
>> template, not a function.
>> You can get this syntax by making the callbacks template arguments,
>> which means they must be known at compile-time. Is that OK with you or
>> do you need the possibility to define the callbacks at runtime?
>
>
> The goal was to do as much as possible at compile time.  Could you elaborate
> on this a bit.  I guess the answer is, yes, it's okay with me.

I mean, it's possible to get a (cb){ some code } syntax, but as that
define a function template, it has no real type: it cannot be a
runtime argument, only an alias template parameter. That means that
all callbacks must be defined in your code, none can come from user
input or runtime computation.


>
>
>> I don't get it: none of your callbacks have a return type per se: they
>> all return 'void'.
>> Do you want callbacks that really return something?
>
>
> Yes, the callbacks at step0 should output a type in the result which is
> specific to step0, and then that type should be fed in as a secondary
> parameter to step1.
>
> I didn't get that far, as I was already stuck.

OK, I get it.



> thanks for your patience!

Well, we are there to explain :-)
I'll have try and code something. If I can get it to work, I'll post it there.