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From Costin Manolache <cmanola...@yahoo.com>
Subject Re: override
Date Thu, 07 Aug 2003 02:43:26 GMT
Thanks for the overview, Nicola !

> Just to get you up to speed, the current issue is about multiple
> inheritance, and how the current system allows cross-import (unwanted?)
> side-effects, as Conor has brilliantly shown.

What I'm not sure I understand is what import has to do with multiple
inheritance :-)

Most of the problems with cross-import and side effects could be resolved by
just using qualified names ( or namespaces ) - like java does to
disambiguate imports. 


> A brief recap of decisions taken IIUC:
> 
> - add an attribute to project: @importable=true, false, only

I hope it is not required, and if it is missing it defaults to true.

> - add possibility of prefix in import declaration
>      <import file="xxx" prefix="xxy"/>

This would work as a "qualified name" ? What's the syntax for the 
prefixed targets/properties ? Any consideration on using XML namespaces 
for this ?

> - all paths are resolved resolved to the importing file basedir

The top-level importing file, or the imediate parent ?

> - keep projectname.ant.file property for relative path resolutions

Good.

> - add <include/> task, like entity includes
> - add <override-target/> task to override targets

Is this "override-target" a substitute for <extends> and OO use of 
ant ( i.e. a buildfile == class, target==method ) ? 

If so, wouldn't be more intuitive to just use the real concept - i.e.
extends and inheritance ?

I know python has a very nice namespacing mechanism where you can replace
or add methods dynamically to an object, but I don't know if this is
desirable for ant. 


> Threads about import (in order):
>     1 - ImportTask ant 1.6
>     2 - ant 1.5.4 : Import
>     3 - override
> 
>  From thread 2 I wrote:
> "
> multi-import(import a,b)
>    target test depends=a.test, b.test
> 
> a
>    target critical
>    target test depends=critical
> 
> b
>    target critical
>    target test depends=critical
> 
> 
> Here "critical" means a.critical to a and b.critical to b, but since
> they reference a generic "critical", they get the only one that remains
> after being redefined. The problem is that I did not redefine it in the
> main buildfile!
> "


Can this be resolved by making all targets qualified after the build file is
read ? 

That would mean ant will see:
 
  top:
    target top.test depends=a.test, b.test

  a
    target a.critical
    target a.test depdends a.critical

  b
    target b.critical 
    target b.test depends=b.critical

After reading any build.xml file, ant will just look at all targets and 
add the project name as a prefix if they don't have one already ( we just
need to agree on the separator syntax ).

When you look at a build.xml, all targets that don't have prefix are
resolved to the current build file - it's pretty easy to understand. 

That mean you won't be able to use import for crazy overrding of 
some targets from one file with targets from other file - but if there is a
real need for that i have no problem with a python-like mechanism where 
you can add/replace methods in an object at runtime. As long as it's 
not disguised as <import> :-)

Costin



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