= Attributes =

Attributes are items of metadata appended to specific program items that end up supplied with your program.[[BR]]

Some of these are given as of standard (Types and Members).[[BR]]

User defined or Custom attributes can be declared and given to specify additional information required or desired.[[BR]]

These attributes provided can be then queried by standard or additional tools or by runtime examination (reflection).

Cobra provides for the declaration and use of attributes similarly to  C# ( on .Net) and Java Language (on Jvm).
These are declared using a keyword prefix ('''has''') with the Attribute (or comma separated Attributes) following 
(similar in form to a cobra Type declaration) rather than a leading syntactic punctuated clause 
(C# square brackets or Java @named-annotation).

Minimally, Attributes can be provided on classes and methods, class Fields and properties.

== Grammar ==

{{{
... has <Attribute>[, <Attribute> ...]
}}}

may be optionally appended to the declaration of a Type (Class, Struct, Interface, Mixin, Enum, Extension, Event, Signature ) or
to a Types Field ('''vars'''), Methods and Properties to provide an Attribute or Attributes on that item.

They can also be given on a methods parameters or an Assembly declaration.

== Examples ==

With respect to GTK

{{{
#!cobra
class NameTreeNode
  has TreeNode(listOnly=true)  # this is an attribute ( with args)

  var name is String
      has TreeNodeValue(column=0)

  def doSomething is protected, override has STAThread
    pass
}}}


In the following, A and B.oldMethod are marked obsolete with the System.Obsolete Attribute.
(This is a .Net common attribute - in cobra it would read better if named '!IsObsolete' or '!ObsoleteMarkerAttribute')
 
{{{
#!cobra
class A has Obsolete("use class B")

    def Method
        pass

class B
    
    def oldMethod has Obsolete("use NewMethod", true)
        pass

    def newMethod
        pass

}}}


== Platform ==

In .Net custom attributes can be defined by defining a class subclassed from System.Attribute.
Attributes are named in Cobra as per declaration and use in C#.


For Java, (.Net) Attributes are known as Annotations. The cobra declaration uses the same prefix but
uses (subclasses) from Java Annotation definitions.


== Reference == 

[http://msdn.microsoft.com/en-us/library/z0w1kczw.aspx C# Attributes][[BR]]
[http://msdn.microsoft.com/en-us/library/sw480ze8.aspx C# Custom Attributes] [[BR]]
[http://msdn.microsoft.com/en-us/library/z371wyft.aspx C#/.Net Common Attributes] [[BR]]


See also:  LanguageTopics