Proposal: user defined attributes

[Manu]

On 19 March 2012 08:46, dennis luehring <dl.soluz at gmx.net> wrote:

>
> attributes does not containing code - there just a (at-runtime) queryable
> information that can be attached to serveral things (like classes, methods,
> ...) - think of it like double.epsilon - but extendable by users - thats
> it, and in the c# world these attribute-definitions tend to be something
> like an class (but without code)
>
> in c# you can walk by (runtime)reflection through your code and find out
> if something is annotated with an special attribute and use the configure
> information and do something with it - call an constructor, open an
> connection, generated code (at runtime) - whatever you want
>
> its a easy-to-use-buildin-**attribution-system thats it - and people like
> them because c# do all the big magic by giving developers a bunch of
> attributes that are then used for stuff like serialization, memory-layout,
> ...
>
> a compiletime example of this could be:
>
> attribute my_special_attribute
> {
>   int version;
> }
>
> attribute my_special_attribute2
> {
>   string test;
> }
>
> class test
> {
>   [my_special_attribute(version=**2)]
>   int method1();
>
>   [my_special_attribute(version=**2)]
>   [my_special_attribute2(test="**bert")]
>   int method2();
> }
>
> void main()
> {
>  auto b = [ __traits(allMembers, D) ];
>  foreach( auto a; b )
>  {
>    -->attribute query magic
>    -->auto c = [ __traits(attribute("my_**special_attribute", a) ];
>    -->auto c = [ __traits(attribute("my_**special_attribute2", a) ];
>
>    //now we know all methods with my_special_attribute
>    //and speical_special_attribute2 and their content (version=2
>    //and test="bert"
>
>    //now think of an template or mixing that uses this
>    //information for code-generation or something like that
>
>    //thats all
>  }
> }
>

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