Ice Docs

Class Inheritance

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Unlike structures, classes support inheritance. For example:

Slice
module M
{
    class TimeOfDay
    {
        short hour;         // 0 - 23
        short minute;       // 0 - 59
        short second;       // 0 - 59
    }


    class DateTime extends TimeOfDay
    {
        short day;          // 1 - 31
        short month;        // 1 - 12
        short year;         // 1753 onwards
    }
}

This example illustrates one major reason for using a class: a class can be extended by inheritance, whereas a structure is not extensible. The previous example defines DateTime to extend the TimeOfDay class with a date.

Classes only support single inheritance. The following is illegal:

Slice
class TimeOfDay
{
    short hour;         // 0 - 23
    short minute;       // 0 - 59
    short second;       // 0 - 59
}


class Date
{
    short day;
    short month;
    short year;
}


class DateTime extends TimeOfDay, Date   // Error!
{
    // ...
}

A derived class cannot redefine a field of its base class:

Slice
class Base
{
    int integer;
}


class Derived extends Base
{
    int integer;                // Error, integer redefined
}

All classes implicitly inherit from Value. This way, a Value parameter in an operation accepts any class instance.