[OE-core] RFC: FOO_subtract, the logical antidote to FOO_append.

[Saul Wold]

On 05/15/2012 11:46 PM, Manuel Bessler wrote:
> Just a few minutes ago I was wondering if such a feature did exist...
>
> I ran into a situation where I wanted to remove something from a .bbappend
> that is added to a variable using VARIABLE_append = "this and that"
>
My understanding is that a _subtract is fraught with danger, there all 
sorts of ordering implications.

For what you are trying to do in a .bbappend, can be done by using 
oe_filter_out() from utils.bbclass, it has to be done in anonymous code.

VARIABLE := "${@oe_filter_out('xxx', '${VARIABLE}', d)}"

This might be what you want.

Sau!

>
> Manuel
> On Tue, May 15, 2012 at 3:01 PM, Peter Seebach
> <peter.seebach at windriver.com>  wrote:
>> There's a few cases where something is a huge list of space-separated
>> things, and it is desireable to remove one.  The example currently
>> afflicting me is DISTRO_FEATURES_LIBC_DEFAULT; I want to end up with
>> the distro features including all but one of the words in it.
>>
>> It seems to me that a counterpart to _append would make sense.  Here
>> is my basic idea:
>>
>> FOO_subtract = "..."
>>
>> means that, when you expand FOO:
>>
>> 1. Fully expand it.
>> 2. Fully expand FOO_subtract.
>> 3. Remove any words in FOO_subtract from FOO.
>> 4. Yield the result.
>>
>> The rationale is that the semantics of things where we're using _append
>> seem to be consistently of the form "this is a space-separated set",
>> and being able to remove things from a set would be Super Handy.
>>
>> So I'm proposing the semantics for consideration, and if people like
>> them, I will go try to implement it in my Copious Free Time.
>>
>> -s
>> --
>> Listen, get this.  Nobody with a good compiler needs to be justified.
>>
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