Object Models

By default, class and interface types on the Island platform are native Island types, adhering to Elements' own object model created specifically for Island. Class types will descend from System.Object or one of it's descendants, forming a single tree of classes.

On some Island sub-platforms, additional, platform-native object and/or interface models are supported. Classes or interfaces defined using these models adhere to a different object model, and live in their own class hierarchy, with classes typically descending from a root object class provided by the platform.

Right now, the following object models are supported:

Island – native Island objects and interfaces; the default
Cocoa – Objective-C objects (descending from Foundation.NSObject) and protocols.
Delphi – Delphi objects (descending from Delphi.System.TObject) and protocols.
COM – to work with COM interfaces
Swift – native Swift objects and protocols.

Darwin

On the Darwin sub-platform for Cocoa, two additional object models are (or will be) supported, in addition to native Island classes. These models are available both for classes and interfaces

Cocoa – Objective-C objects (descending from Foundation.NSObject) and protocols.
Swift – Native Swift objects (descending from Swift.Object) and protocols.

The Darwin sub-platform provides full support for the Objective-C class model, as needed to interact with the core Cocoa APIs from Foundation over AppKit/UIKit to more specialized frameworks provided by Apple and third parties.

Note: The Swift object model is not to be confused with using the Swift language dialect provided by Silver. As with all five OOP Elements languages, classes written in Silver can be native Island classes, Objective-C Runtime classes or, optionally, Swift Runtime classes.

Delphi

On selected platforms (currently desktop Windows, Linux and macOS, Elements is introducing support for working directly and natively with types and APIs from Delphi-built packages.

Delphi – to work with Delphi-build packages, types and APIs.

Refer to the upcoming Delphi SDKs topic for more details.

Delphi support is limited to platforms and architectures your particular version of Delphi supports, and will for now not extend to mobile platforms.

Note: Delphi SDK support is still highly experimetal

COM

While mostly useful on the Windows platform, Interface types on any Island sub-platform can, optionally, be cdeclared as COM-compatible interfaces for interaction with other COM-compatible environments.

COM for declaring and using COM-compatible interfaces based on IUnknown.

Please refer to the COM topic for more details.

Mixing Object Models

Objects and interfaces from the different object models can freely interact with each other. Classes declared in one model may have fields, properties or method parameters of the other model, and the interaction will work seamlessly as one would expect.

The same interfaces can be implemented by classes of either model, allowing code to interact with the types without needing to be aware of the underlying class model – even though the classes themselves do no share a common ancestor. Similarly, Island-native generics can be used with classes or interfaces of either model, seamlessly and without runtime overhead (e.g. an Island-native List<T> may be instantiated to hold Cocoa objects, Island Objects or Swift objects).

Automatic wrapping and unwrapping will happen when assigning objects to a base Object/NSObject/TObject-type variable of a different object model, using wrapper classes provided by Island RTL, such as CocoaWrappedIslandObject et al, but this will rarely affect strongly typed user code.

Default Object Model

As indicated above, the default object model for classes and interfaces normally is the native Island object model, and classes and interfaces without ancestor will become part of this model.

A new "Default Object Model" Compiler Option is provided to change that. By setting this option to, e.g., "Cocoa", classes and interfaces declared without ancestor will become Objective-C types by default instead, making the compiler behave much like the classic Cocoa platform, where all classes were based on the Objective-C runtime.

This option is useful when writing code that is highly Cocoa-centric (such as macOS or iOS GUI apps), and best used with the New Cocoa Mode that provides additional compatibility with classic Cocoa projects.

Of course Cocoa classes in this mode can still freely interact with native Island types and Swift Runtime types, as described in the previous section.

The same goes for setting a default object model of "Delphi" or – later, when fully supported – "Swift".

Note that the default object model only applies to types declared without explicit ancestor. Classes that declare an ancestor will automatically be of the same object model as said ancestor, so for example inheriting a class from TObject (or any of its descendants, such as TForm) will automatically make it a "Delphi" object model class.

Instead of providing an ancestor, you call also specify a class's object mode by attaching its model as an Aspect.

Standard Types

Setting a default object model also brings the RemObjects.Elements.System.ObjectModel namespace into scope (where ObjectModel is the actual name, e.g. RemObjects.Elements.System.Island or RemObjects.Elements.System.Cocoa. This is how Common standard type names (mainly Object, String and Exception) get mapped to their appropriate model.

For setting the default to "Cocoa" brings RemObjects.Elements.System.Cocoa.String into scope, which aliases to NSString; setting it to "Delphi" brings in RemObjects.Elements.System.Delphi.String, which aliases to DelphiAnsiString or DelphiUnicodeString, depending on version, and RemObjects.Elements.System.Delphi.Object, which aliases to TObject.

In C#, the object and string keywords will map to whatever Object or String type is thus in scope.

Determining a Type's Model

The modelOf() system function accepts as its single parameter the name of a specific type know at compile time or a generic type parameter in scope, and returns a string value describing it's model, currently one of Island, Cocoa, Swift Delphi or COM.