[Development] [Feature] Q_INFO: Annotations for classes, methods, properties and enums

[Thiago Macieira]

On terça-feira, 10 de setembro de 2013 18:26:09, Stefan Merettig wrote:
> Alright guys, let's try to complete the feature. As I heard from sides
> now that you want a key-value store, I'll do it that way.
> 
> Feature list:
> 1. Q_INFO is a new macro (which expands to nothing):
>    #define Q_INFO(key, value)
> 2. Q_INFO can be prepended to:
>   - Classes

We have Q_CLASSINFO for that.

>   - Signals, slots and Q_INVOKABLE methods (This includes c'tors)
>   - Q_PROPERTY

Other people have suggested adding the info to the Q_PROPERTY expansion. This 
would avoid a sequence of Q_INFO / Q_PROPERTY pairs in the class that might be 
difficult to read:

	Q_INFO("foo", "bar")
	Q_PROPERTY(int bar READ bar)
	Q_INFO("foo", "baz")
	Q_PROPERTY(int baz READ baz)


>   - Q_ENUM'd enums
>   - So everything that is accessible through the meta system
> 3. Multiple Q_INFO annotations for a single object are possible
> 4. Each object has a unique key -> value mapping. This means, that
> something
>     like: Q_INFO("a", "b") Q_INFO("a", "c") void myFunc(); results in a
> single
>     key -> value mapping, not two values for "a".

Why?

> 5. API Design: Pretty much a copy of QMetaClassInfo from the user
> standpoint,
>     the class will be called QMetaInfo.
> 
> Questions:
> 1. If Q_INFO can be applied to classes, then it's redundant to
> Q_CLASSINFO.
>     On the one hand it's nice to have a unified API for annotations, on
> the
>     other hand it's redundant, as Q_INFO doesn't have any benefits over
>     Q_CLASSINFO anymore.

I prefer Q_CLASSINFO.

> 2. How should we store this? My current approach still stems from when
> Q_INFO
>     supported multiple arguments. Technically possible, but not liked.
> As Thiago
>     pointed out: JSON is out of the question. I'd like to stick to
> something like
>     my current implementation. It boils down to having a table in the
> meta_data
>     array with two columns for each object: start index, count
>     At 'start index' there's a list of two integers for each Q_INFO
> record, the
>     first pointing to the name, the second to the value. I'd like to use
> a third
>     column there to store a currently unused "flag". In my initial
> implementation
>     which is also on gerrit I have a fourth field to store the value
> count, but
>     with only a single one this can obviously be dropped if we don't
> plan to ever
>     support this feature.

Keeping an unused "flag" field is a good idea.

How do you associate the method ID or property ID with an info?

-- 
Thiago Macieira - thiago.macieira (AT) intel.com
  Software Architect - Intel Open Source Technology Center
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