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>]...]
[<DocString>]
[
[<Variables>]
[<Properties>]
[<Methods>
[<ClassEnums>]
[<Sigs>]
[<Invariants>]
[<Tests>]
[<SharedClause>]
]...
# empty (placeholder) class
class <ClassName>
[is <AccessModifiers>]
[has <Attributes>]
[where <GenericParam> must be <GenericConstraints>]
[inherits <BaseClassName> ]
[implements <InterfaceName> [, <InterfaceName>]...]
[<DocString>]
pass
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>] ]
[<DocString>]
var <variableName> [as <Type>] [= <initialValue>]
[is <AccessModifiers>]
[has <Attributes>]
[<DocString>]
e.g.
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
e.g.
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
Properties
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>] ]
[<DocString>]
set <propName> [ as <Type>] [from {var, <backingVariableName>} [= <initValue>] ]
[<DocString>]
pro <propName> [ as <Type>] [from {var, <backingVariableName>} [= <initValue>] ]
[<DocString>]
# full accessor variant, one or both of 'get' and 'set blocks must be present.
pro <propName>
get
[...]
return <value>
set
[...] # 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 pro get return _x set _x = value
Methods
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>]
[<DocString>]
def <methodName>(<paramList>) [as <returnType>] [is <AccessModifiers>]
[has <Attributes>]
[<DocString>]
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?
e.g.
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.
TBD
Generics
accessing baseclass methods
Example
class SimplestClass pass class VeryMinimal """ Docstring for class """ cue init base.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.
#Interfaces 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 #shared #_lifespan = 8 cue init _age = 1 .liveWeight = 2 _isAlive = true def makesNoise as String return 'Baaaaa' pro mateName as String get return 'Ram' set pass pro childName as String get return 'lamb' set pass 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]' s.age(1)
See also: Cue, LanguageTopics
