Class Definitions

A class provides the definition for the type of an object and the variables, properties, events, and methods that the class comprises.
In addition it may declare tests to exercise the class and contracts or constraints the class must conform to to ensure continuing validity.

Classes are declared using the class keyword followed by the name of the class.
The classname must start with an uppercase letter.

The class may have any of the usual access modifiers.
The Superclass inheritance and interface conformance are indicated with the inherits and implements keywords.
Attributes metadata can be specified with the has keyword.

Class Grammar

class <ClassName>  
    [is <AccessModifiers>]
    [has <Attributes>]
    [where <GenericParam> must be <GenericConstraints>]
    [inherits <BaseClassName> ]
    [implements <InterfaceName> [, <InterfaceName>]...]


# empty (placeholder) class
class <ClassName>  
    [is <AccessModifiers>]
    [has <Attributes>]
    [where <GenericParam> must be <GenericConstraints>]
    [inherits <BaseClassName> ]
    [implements <InterfaceName> [, <InterfaceName>]...]

Instance and Class Variables

Instance and Class variables are declared within the class using keyword var followed by the var name.
Like local variables they may be explicitly typed ( as <Type> ) and if not are defaulted to type dynamic.

An initial value may be specified (if not the var gets its types 'empty' value ( 0, "" or nil)
(Idiomatically its usually preferable to explicitly initialise the var and not explicitly specify the Type).

AccessModifiers usually specifying visibility can be given.
Attributes providing metadata can also be given.

Instance and Class variable definition Grammar

    var <variableName> [as <Type>] [= <initialValue>] [is <AccessModifiers> [has <Attributes>] ]

    var <variableName> [as <Type>] [= <initialValue>]
        [is <AccessModifiers>]
        [has <Attributes>]


    var x as String
    var _y as int
    var _ya as int = 47
    var z as int is private
    var t as int = 99
        is protected, shared
        """t is a Temporary backup value"""

All class and instance variable names must start with a lowerCase Letter

If the name is prefixed with an _ (single underscore) its accessType defaults to protected and it is directly accessible from within the class method code.

If the name is prefixed with an _ _ (double underscore) its accessType defaults to private and it is directly accessible from within the class method code.

Without that prefix on the name the variables accessType is public (by default) and it must be accessed from within method code by prefixing the name with either this. or just . .

In either case the default access setting can be adjusted with an access modifier clause.

Class (or static) variables are specified with the access modifier shared as in is shared

    var _x = 100  # default protected
    def tryx( opnd as int) as int
        return _x + opnd

    var __x = 200 # default private
    def tryPrivx( opnd as int) as int
        return __x + opnd

    var y is protected  # default public, explicit access modifier overrides setting to protected
    def tryy( opnd as int) as int
        return .y + opnd

    var statX as int = 45
        is shared
    def x 
        print .statX


This discussion is somewhat simplified for clarity.
Please see Properties

Properties are members that provide a flexible mechanism to read, write, or compute the values of private fields.
They are used as if they are public data members, but are actually implemented via special methods called accessors.

There are 3 keywords for defining a property:
get defines a readOnly property ( Can access the properties value but cant change it).
set defines a writeOnly property (Can write to the property but cant read it)
pro defines a readable and writable property.

If a property accessor merely reflects a protected or private backing variable (field) you can
use a clause beginning with keyword from.

  • from var
    pro <name> from var or get <name> from var or set <name> from var
    The property will get or set its value unchanged from a backing variable named to the property name with a single underscore prepended to it.
    • If there is no backing variable but there is an assignment to the property or a type declaration on the property the backing variable will be implicitly created for you.
  • from <backingVarName>
    Otherwise the word following the from must be the name of an existing backing store variable.

Finally if an accessor needs to translate, filter or modifies in some way a backing variable or computes a value
there is a longer syntax variant where either of both the get and set accessors can be specified and a block of code
provided to store (setter) or generate (getter) the property value.

(Simplified) Properties Grammar

get <propName> [ as <Type>] [from {var, <backingVariableName>} [= <initValue>] ]

set <propName> [ as <Type>] [from {var, <backingVariableName>} [= <initValue>] ] 

pro <propName> [ as <Type>] [from {var, <backingVariableName>} [= <initValue>] ] 

# full accessor variant, one or both of 'get' and 'set blocks must be present.
pro <propName> 
        return <value>
        [...] # assign or otherwise do something with implicit arg "value" (passed in) 

Property Example

var _x  = 47
pro x from var     # property x uses backing var _x
# above same as 
#pro x from _x

Can do all of the above in one line like

pro x from var = 47
# or
pro x from var as int = 47

Above is equivalent to fully specified accessor form

var _x = 47
        return _x
        _x = value


A method is a code block that contains a series of statements.
A program causes the statements to be executed by calling the method and specifying any required method arguments.

Methods are defined using the keyword def.

If not specified the returnType is void ( i.e nothing returned) and the access modifiers are public, virtual

Like variables if the name is prefixed with an _ its access modifier defaults to protected, virtual and it is directly accessible from within the class method code.
If the name is prefixed with an _ _ (double underscore) its access modifier defaults to private',virtual' and it is directly accessible from within the class method code.

Without those prefixes on the name of the methods the accessType is public, virtual and it must be accessed from within method code by prefixing the name with either this. or just . .

Method Grammar

    def <methodName> [as <returnType>]  [is <AccessModifiers>]
        [has <Attributes>]
    def <methodName>(<paramList>) [as <returnType>]  [is <AccessModifiers>]
        [has <Attributes>]

The initializer or constructor method of a class is a special method called init which is implicitly called when a class instance is constructed. Its responsible for setting the contents of a class instance to an initial state. It doesnt return any value and is not inherited (i.e baseclass initialization must be done with an explicit call to a baseclass constructor).

If an init method is not specified the compiler runtime generates a noArg constructor that does nothing. Because this method is 'special' it is declared using cue rather than def. See cues?

Constructor chaining must be done explicitly to another constructor in the same class (usually with a different number or Type of args) or to a Superclass constructor (using base.init) - this call must be the first executable line in the init method.

Method Parameter List

A parameter list is a comma separated list of name (and optionally type and parameter description modifier) specifications

<paramName> [as [<paramDesc>] <Type>]  [, ...]

<paramDesc> is optional and may be vari and/or a parameter direction indicator out or inout ( default if unspecified is in)

vari indicates the parameter name is a placeholder for a variable length arglist. Within the method this may be unpacked/accessed as a list.

in (implicit) Args are only passed into the method. Any changes made to the argument inside the method are not visible outside the method (pass-by-value)

out the arg is returned from the method

inout argument is both passed into the method and (any possibly changed) value is also returned from the method (pass-by-reference)

If <Type> is unspecified it is treated as dynamic?


    def meth( a, b is String, c is out String)
        c = b + "_meth"

    def sum(a as vari int) as int
        sum = 0
        for i in a
            sum += i
        return sum

meth takes 3 args , the first and second are inward only and are dynamic and a string respectively, the third is only returned from the method as a string.
sum takes a variable number of integer args.



accessing baseclass methods


class SimplestClass

class VeryMinimal
    """ Docstring for class """

    cue init  
        # Above is equivalent to no initialiser at all
        # .... rest of initialiser code

    def aMethod
        print 'in aMethod of class [this]'
        # more method code

A more extended example.

interface Audible
    def makesNoise as String

interface Mateable
    pro mateName as String

interface Breedable
    inherits Mateable 

    pro childName as String

# class declaration - note indentation
class Bovidae
    def diet as String
        return 'Herbivorous Cud Chewing'
    def numHooves as int
        return 4

class Sheep 
    is public, nonvirtual    # public is default anyway
    inherits Bovidae        # Superclass
    implements Audible, Breedable
    var _lifeSpan as int = 8
         is shared               # years average
    # or var lifeSpan as int private shared

    var _age as int =1
    var liveWeight as int is private
    var _isAlive as bool
    #_lifespan = 8  
    cue init
        _age = 1
        .liveWeight = 2
        _isAlive = true

    def makesNoise as String
        return 'Baaaaa'

    pro mateName as String
            return 'Ram'
    pro childName as String
            return 'lamb'

    def age(byNYears as int)
        _age += byNYears
        if _age > _lifeSpan
            _isAlive = false

    def gainWgt(wgt as int)
        .liveWeight += wgt

    def toString as String is new
        return 'Sheep:age=[_age], weight=[.liveWeight], living=[_isAlive]'
    def main is shared
    s = Sheep()
    print 's=[s]'

See also: Cue, LanguageTopics