= Access Modifiers =

Access Modifiers can be specified  on Classes, class (instance and class) variables and methods to set their visibility and accessibility[[BR]]
These are also called 'isNames' in the Cobra doc and discussion since they're specified with a leading '''is''' keyword.

Method Access modifiers
    '''virtual, public''' is default for methods[[BR]]

    '''protected''' is default for methods and  class/instance variables with '''_''' prefix on name[[BR]]
    '''private''' is default for methods and class/instance variables with '''_ _''' (double underscore) prefix on name[[BR]]
    '''public''' is default for variables without any '''_''' prefix

Valid 'is' keywords are 
 *       '''fake''' - specifies item has no implementation - a placeholder (deprecated in favor of '''extern''')
 *       '''shared''' - Specifies Class (static) method or variable, 
 *       '''virtual''',   '''nonvirtual''' -  on methods, specifies that the method is overridable or not 
 *       '''override''', '''new'''         -  on methods specifies that a method is overriding or replacing a baseclass method of the same signature
 *       '''public''', '''protected''', '''private''', '''internal''' - specifies item visibility 
 *       '''abstract''' - specifies a template only, subclasses must define fully
 *       '''extern''' - item has no implementation and is defined elsewhere (outside a cobra file)
 *       '''partial''' - on class types - specifies that the type is defined across multiple files 				 
 *       '''readonly''' specifies that a variable or field cannot be modified. 
            It must be initialised as early as possible and cannot have its value modified after.

Separate multiple modifiers with ''',''' e.g    ....  is protected, override



== Item Visibility ==

Visibility (or accessibility) denotes the access to types or type variables (fields) 
 * public    -  the most permissive access level. There are no restrictions on accessing public members or public types.
 * protected - access is limited to the containing class or types derived from the containing class.
 * private   - access is limited to the containing type.
 * internal  - access is limited to the current assembly (or packaging entity).

These modifiers cannot always map exactly as specified to backend supported visibility layers so best to treat them as decreasing
levels of advisory visbility as given above.
   
== Notes and Examples ==

    * is extern::
       - temporary for defining class/method api without implementation
e.g
{{{ 
#!cobra
class TextWriter is extern

    get newLine as String
        pass
}}}
   
    * is shared::
        - on instance variable makes it a class variable.
        - on method makes it a class method
        -     (effect is same as static (in C#, Java))
e.g
{{{ 
#!cobra
class Runner
   def main is shared
      print 'main class for Runner'
}}}

    * is public/protected/private/internal::
         - on class, instance variable or method(s)
         - adjust visibility (default public)

    * is abstract::
        - on class or method(s)
        - Specifies item as a template for subclasses to provide a concrete implementation of.

    * is virtual::
       - method is redefinable/subclassable (default)

    * is nonvirtual::    
        - method is not redefinable, cannot be subclassed.

    * is override::
        - on a method
        - Specifies that this method implementation is a redefinition of an existing(shadowed virtual or abstract) method defined in a superclass

    * is new::
       - on a method 
       - designate that this method is a new one that hides the one that would have 
        been inherited from a baseclass.
        e.g
{{{
#!cobra
class Vehicle

    def drive is nonvirtual
        pass

class Car inherits Vehicle

    def drive is new  # replaces superclass method
       pass
}}}

When a method, property or indexer has the same name and type signature as a base member, 
you must specify '''is override''' or specify '''is new''' 
or use '''base.''' in the implementation (which is an implicit '''is override''')   


    * is partial::
       - on class types ( class, structures, interfaces)
       - indicates that the type is defined across multiple files. Each piece so defined must be so tagged. 
       - Idiomatically the first file compiled should have the full declaration (inheritance, attrinutes etc) and the remainder have only the access modifies ( including 'partial')

    * is readonly::
      - on variables (local and type)
      - indicates that the variable cannot have its value changed
      - the variable must be assigned to (explicitly initialised) on declaration or (for class type variables) must be initialised in the classes initialiser method.

== See also ==
[http://msdn.microsoft.com/en-us/library/vstudio/wxh6fsc7.aspx C# reference Access Modifiers]

[http://msdn.microsoft.com/en-us/library/ba0a1yw2%28v=vs.71%29.aspx C# Accessibility Levels]

[http://docs.oracle.com/javase/tutorial/java/javaOO/accesscontrol.html Java Access Modifiers]