= Access Modifiers =

Access Modifiers can be specified  on Classes, (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.


Valid 'is' keywords are 
 *       '''fake''' - specifies item has no implementation - a placeholder (deprecated in favor of '''extern''')
 *       '''extern''' - item has no implementation and is defined elsewhere (outside a cobra file) (replaces/preferred to '''fake''')
 *       '''shared''' - Specifies a 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 the class or method is a template only, subclasses must define fully
 *       '''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

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



== Class is-names ==
    classes  and interfaces are '''public''' by default[[BR]]

 *       '''fake''' - specifies class has no implementation - a placeholder (deprecated in favor of '''extern''')
 *       '''extern'''  - class has no implementation and is defined elsewhere (outside a cobra file) - replaces '''fake'''.
 *       '''shared''' - Specifies that the entire class is made of static methods and  (class) variables, 
 *       '''public''', '''protected''', '''private''', '''internal''' - specifies the class visibility (default is '''public''') 
 *       '''abstract''' - specifies the class is a template only, subclasses must define fully
 *       '''partial'''  - specifies that the type is defined across multiple files 				 

== Method is-names ==
    methods are '''virtual, public''' by default[[BR]]

    Methods prefixed with '''_''' on their names  are '''protected''' by default[[BR]]
    Methods prefixed with   '''_ _''' (double underscore) on their names are '''private''' by default.[[BR]]
    Methods with no underscore prefixes are '''public''' by default.

 *       '''fake''' - specifies method has no implementation - a placeholder (deprecated in favor of '''extern''')
 *       '''extern''' - method has no implementation and is defined elsewhere (outside a cobra file) (use instead of '''fake''')
 *       '''shared''' - Specifies a class (static) method, 
 *       '''virtual''',   '''nonvirtual''' -  specifies that the method is overridable or not 
 *       '''override''', '''new'''         -  specifies that a method is overriding or replacing a baseclass method of the same signature
 *       '''public''', '''protected''', '''private''', '''internal''' - specifies item visibility 
 *       '''abstract''' - specifies the method is a template only, subclasses must define fully

== Type variables or fields is-names ==

    These are '''virtual, public''' by default[[BR]]

    Type variables prefixed with '''_''' on their names  are '''protected''' by default[[BR]]
    Type variables prefixed with   '''_ _''' (double underscore) on their names are '''private''' by default.[[BR]]
    Type variables with no underscore prefixes are '''public''' by default.

 *       '''shared''' - Specifies a class (static) variable (rather than an instance variable), 
 *       '''public''', '''protected''', '''private''', '''internal''' - specifies item visibility 
 *       '''readonly''' specifies that a variable or field cannot be modified once initialised. 
         *   It must be initialised as early as possible and cannot have its value modified after.




== 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 a class/method API without implementation
e.g
{{{ 
#!cobra
class TextWriter is extern

    get newLine as String
        pass
}}}
   
    * is shared::
        - on a variable/field of a type 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, type 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::
        - on a method
        - method is redefinable/subclassable (default)

    * is nonvirtual::    
        - on a method
        - method is not redefinable, cannot be redefined or overridden.

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

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

    def drive is nonvirtual
        pass

    def steer # virtual by default

class Car inherits Vehicle

    def drive is new  # replaces superclass method
       pass

    def steer is override # is override must be specified to indicate planned override of virtual baseclass method
}}}

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, attributes 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]