Type conversion

zoop supports type conversion between parent classes, subclasses, and interfaces. Type conversion is divided into two types:

• Static conversion: users can confirm successful conversion. If the user makes a mistake, a compile error or @panic will appear.
• Dynamic conversion: Conversion failure will not cause compilation errors or @panic, the conversion result will just be null

Static conversion

Static conversion is performed through the cast() method of the class. Two types of static conversion are supported:

• Subclass pointers can be statically converted to parent class pointers (but not vice versa)

var sub: *SubClass = try SubClass.new(allocator);
var base: *Basic = sub.cast(Basic);

• Class pointers can be statically converted to any implemented interface

var sub: *SubClass = try SubClass.new(allocator);
var iobj: zoop.IObject = sub.cast(zoop.IObject);
var ibas: IBasic = sub.cast(IBasic);

Note

For static conversion from a class to an interface, the class must be the object pointed to by rootptr. For example:

var sub: *SubClass = try SubClass.new(allocator);
var base: *Basic = sub.cast(Basic);

In the above code, sub is the object pointed to by rootptr, but base is not, because base actually points to sub.mixin.data.modname_Basic.

Dynamic conversion

Dynamic conversion is performed through the as() method of the class and the as() method of the interface. It supports conversion between classes and interfaces in four ways:

var sub: *SubClass = try SubClass.new(allocator);

// 1 class to class
var bas: ?Basic = sub.as(Basic);
sub = bas.?.as(SubClass).?;

// 2 classes to interfaces
var iobj: ?zoop.IObject = sub.as(zoop.IObject);

// 3 interface to interface
var ibas: ?IBasic = iobj.?.as(IBasic);

// 4 interface to class
sub = iobj.?.as(SubClass).?;
bas = iobj.?.as(Basic);

Note

• Dynamic conversion requires an array search operation, which is not 0 cost. Static conversion only requires pointer operations, which is almost 0 cost.
• Dynamic conversion does not require the object to be the object pointed to by rootptr