Re: my take on ZCML's includeOverrides

On Tue, Dec 7, 2010 at 1:57 PM, Chris McDonough <[email protected]> wrote:
> Independent of my previous call for discussion about ZCML conflict
> resolution, I'm cutting and pasting my side of a discussion about the
> ZCML "includeOverrides" directive from an IRC chat, because it may come
> in useful for folks grappling with its behavior.  There's not really any
> human-consumable docs about it.
>
> If I've made any mistakes, please let me know.
>
> [13:42] <mcdonc> so ftr, i've found that ZCML's includeOverrides and
> include to do (at least on one vector) exactly the opposite of what you
> might expect them to do
> [13:42] <mcdonc> "includeOverrides" is a poor name
> [13:42] <mcdonc> what it does is to emulate the behavior of inlining
> stuff into the file you use it from
> [13:43] <mcdonc> when you use includeOverrides it's as if you typed all
> the directives in the included file into the file you're including from
> [13:43] <mcdonc> otoh, "include" doesnt behave like this
> [13:44] <mcdonc> you can actually define the same directive in three
> files
> [13:44] <mcdonc> configure.zcml, one.zcml, and two.zcml
> [13:44] <mcdonc> and if you use "include" from configure.zcml of one and
> two
> [13:44] <mcdonc> there will be no conflict
> [13:45] <mcdonc> this is because non-conflicting "rootmost" directives
> win
> [13:45] <mcdonc> otoh, if you use includeOverrides of one and two from
> configure.zcml
> [13:45] <mcdonc> all three will conflict
> [13:45] <mcdonc> because its as if you typed them all in configure.zcml
> by hand
> [13:45] <mcdonc> and that means there are three conflicting rootmost
> directives
> [13:46] <mcdonc> if you mentally substitute "inline" for
> "includeOverrides" it makes a little more sense

Maybe.  It described the mechanism better, but includeOverrides conveys the
intent. <shrug>

> [13:48] <mcdonc> override is exactly the wrong phrase to use in the name
> of this directive
> [13:51] <mcdonc> what it boils down to is that you never, ever really
> want to use includeOverrides except in your rootmost zcml file
> [13:51] <mcdonc> and probably not even there
> [13:51] <mcdonc> because you can get the same effect by typing the
> directives there by hand

Why would you want to type the directives by hand?

I've used includeOverrides in cases where:

1. I want to use 2 high-level components, one of which
    customizes the other, or in which

2. I wanted to organize overrides in various ways where I
    don't want to put everything in a root (or high-level file).

Of course, you can sometimes get the same effect in other ways.
For example, if one high-level component overrides another, then
the overriding component can just include the overridden one.

Jim

-- 
Jim Fulton
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