root/cobra/trunk/HowTo/111-UseProperties.cobra

"""
This program shows how to declare and use properties.
Property declarations always start with one of three keywords:
    * pro
    * get
    * set
"""


class Person

    var _name as String

    cue init(name as String)
        base.init
        _name = name

    pro name as String
        """
        The name of the person. Setting the name trims preceding and
        trailing whitespace from the value.
        """
        get
            return _name
        set
            # `value` is an implicit argument in all property setters:
            _name = value.trim

    def printName
        print .name

    def sayHello
        print 'Hi, my name is [.name]'


class Program

    def main
        p = Person('chuck')
        print p.name
        assert p.name == 'chuck'
        p.name = 'Chuck'


# Many properties just cover for an underlying variable. When that
# is the case, you can use a shortcut syntax. Later, you can
# change the property to the full form in order to add logic.

# In this shortcut syntax, properties and their backing vars are
# declared in one line:

class Person2

    cue init(name as String)
        base.init
        _name = name

    pro name from var as String
    
    pro age from var as int


# You can even pack an initial value into the declaration
# which also be used to infer the data type.

class Person3

    pro name from var = ''  # inferred as String
    
    pro age from var = 0    # inferred as int


# In this shortcut syntax, the vars were already declared so
# the property simply "... from var":

class Person4

    var _name as String
    var _age as int

    cue init(name as String)
        base.init
        _name = name

    pro name from var
        """
        The "from var" indicates that the type of the property, as well
        as its value, is taken from the class variable with the matching
        name (underscore + property name). When you later want to add
        code for this property, just chop off the "from var" and write
        the full property (pro foo as Type; get ...; set ...)
        """

    pro age from var


# If the underlying variable name is different than the property name,
# you can specify that name instead of "var":

class Person5

    var _name as String

    cue init(name as String)
        base.init
        _name = name

    pro nombre from _name


# Properties can be read-only:

class Person6

    cue init(name as String)
        base.init
        _name = name

    get name from var as String

    get lowerName as String
        return _name.toLower


# Properties can be write-only:

class Parts

    var _stuff = List<of Object>()

    set contents as List<of Object>
        _stuff.clear
        for item in value
            _stuff.add(item)


# Properties can be protected, typically with an underscore, although
# it's not very common. Then only this class and subclasses can invoke
# them:

class Foo

    get _mol as int  # underscore implies `protected`
        return 42

    get goldenRatio as number is protected   # `protected` can be explicit
        return 1.618033989

    def doSomething
        # Note that when accessing underscored members, you no longer
        # use the preceding ".":
        assert _mol == 42

        # Without an underscore, the "." is required:
        assert .goldenRatio > 1.6