= Interface Definition =

An interface defines a feature set or related functionality as a small group of 
properties, methods, and events.

A class or struct '''implementing''' an interface provides a concrete implementation for 
all of the members defined by that interface.  

An Interfaces members are automatically public.

The interface itself provides no functionality (implementation) that a class or struct 
can inherit the way that base class functionality can be inherited. 
(Instead see [wiki:Mixins mixins])[[BR]]
However, if a base class implements an interface, any derived class inherits that
implementation (and thus continues to implement that interface).

    * An interface is like an abstract base class:[[BR]] 
      any non-abstract type inheriting the interface must implement all its members.
    * An interface cannot be instantiated directly.
    * Interfaces contain no implementation of methods or properties.
    * An Interface cannot contain fields.  
    * Classes and structs can inherit from more than one interface.
    * An interface can itself inherit from multiple interfaces.


In Cobra, Interfaces are declared using the '''interface''' keyword followed by the 
interface name. [[BR]]
The interface  may have any of the usual [wiki:AccessModifiers access modifiers] and
interface hierarchies (!SuperInterfaces) can be specified using '''inherits'''

Interfaces can have attributes and may be declared as generic with constraints.

Use of a docstring on Interfaces is encouraged.


=== Interface Grammar ===
{{{
# The grammar elements below are ordered for simplicity but the compiler will accept 
# those elements in any reasonable order.

interface <InterfaceName>  
    [is <AccessModifiers>]
    [has <Attributes>]
    [where <GenericParam> must be <GenericConstraints>]
    [inherits <BaseInterfaceName> [, <BaseInterfaceName>]... ]
    [<DocString>]

    [ 
        [<Properties>]
        [<Methods>
        [<Events>]
}}}

== Example ==

This example declares an interface, IDimensions, and a class, Box,[[BR]]
which explicitly implements the interface members getLength and getWidth.

The members are accessed through the interface instance dimensions.
{{{
#!cobra
interface IDimensions
    """ Interface for Dimensions of a 2D object"""
    def getLength as float
    def getWidth as float

class Box implements IDimensions
    var lengthInches as float
    var widthInches as float

    cue init length as float, width as float)
        .lengthInches = length
        .widthInches = width

    # Explicit interface member implementation: 
    def getLength as float
        return .lengthInches
        
    def getWidth as float
        return .widthInches

    def main is shared
        #// Declare a class instance box1:
        box1 = Box(30.0f, 20.0f)

        #// Declare an interface instance dimensions:
        dimensions = box1 to IDimensions

        #// Print out the dimensions of the box by calling the methods 
        #// from an instance of the interface:
        print 'Length: [dimensions.getLength]'
        print 'Width:  [dimensions.getWidth]'
    }
}
/# Output:
    Length: 30
    Width: 20
#/

}}}



Using generics
{{{
#!cobra
interface IEquatable<of T>
    """Interface for an object that can tell if it is equal to other objects of the same type"""
    def equals(obj as T) as bool


class Car implements  IEquatable<of Car>
    pro make as String
    pro model as String
    pro year as String

    #// Implementation of IEquatable<of T> interface
    def equals(car as Car) as bool
        if .make == car.make and .model == car.model and .year == car.year
            return true
        return false
}}}


== Notes ==


[wiki:LanguageTopics Back to LanguageTopics]