On Friday, 28 February 2014 at 18:42:57 UTC, Steve Teale wrote:
All the D aficionados seem to wet their pants over
meta-programming, but I struggle to find a place to use it.
IIRC, I used it in a couple of places when I was trying to write
library stuff for MySQL, but in my current project, I use it
only
once. That's when I want to stuff something onto my undo stack.
For that I have two template functions - push(T)(MybaseClass* p,
T t, int ID), and pushC, which is just the same except that it
checks the top of the stack to see if the ID there is the same
as
what it is wanting to push.
This has served me very reliably, but I struggle to find other
places in the whole application where I would benefit from
templates.
Is this typical - libraries use templates, applications don't,
or
am I just being unimaginative?
Yes.
Templates are awesome. I use them when ever I can. They allow you
to simplify the tasks.
If you check out my thread about dependencies you can see a good
example.
iGui --> iButton
|
|
|> WindowsGui --> WindowsButton
|
|> LinuxGui --> LinuxButton
When programming to interfaces you lose the ability to use
concrete types easily. E.g., WindowsGui can't use a WindowsButton
because it has to implement iGui, which uses iButton... even
though WindowsButton is an iButton and the only one we want to
use with WindowsGui.
But as far as WindowsGui is concerned, there is no iButton but
just a WindowsButton(Because it doesn't care about being
general... and doesn't care about LinuxButton, RogueButton, or
whatever).
In some sense, iButton was meant to be used with iGui and
WindowsButton for WindowsGui... but we can't do this easily in
D... well, unless you use a template to generate all the crap
code you would normally have to write.
So a template(compile time construction) can help do things
easier than you could otherwise... and if you do them right they
are generic enough to be used in general things. (like anyone
could use the template I created to help them with the same type
of problem)
You are missing the point because the whole reason templates are
generally used in libraries is because they are so powerful(you
want to reuse them).
In the example I give above, the mixin template reduces code
bloat and error proneness significantly for large classes and
makes you feel like you are writing classes like you would
normally write them when not using interface programming.
Basically until you start using templates a lot you won't know
where to use them in the first place. You just gotta get used to
them and then you'll start trying to use them everywhere.
(granted, I'm using mixin templates but templates nonetheless)
