[meta] Implement typed objects

[trev]

Background

One way to improve performance and memory efficiency would be ​typed objects. Now this proposal isn't implemented in any browsers yet, also the proposal doesn't match our needs exactly. So we should create our own implementation, a subset of the proposal with a few deviations:

• Implement ClassType rather than StructType. Properties with functions as their values should turn into methods. An additional parameter should specify metadata, e.g. constructor and destructor functions.
• Classes should inherit from each other, with the TypedObject class being the common ancestor. For any property requiring a class as value it should be possible to use its subclass.
• Instantiation using type.new() instead of callable types - the latter would require messing with the deprecated __proto__ property which shouldn't be worth it.
• No automatic garbage collection (cannot be implemented), instead all objects should have a .free() method to trigger manual destruction.
• A string type needs to be implemented as an array of uint16 characters.
• Dictionary types need to be implemented in addition to array types: string keys, a fixed type as value.

What to change

Ticket	Status	Resolution	Summary	Owner
#147	closed	fixed	[Typed objects] Implement object types	trev
#148	closed	rejected	[Typed objects] Implement fixed-size array types
#149	closed	rejected	[Typed objects] Implement dictionary types	trev
#150	closed	fixed	[Typed objects] Implement string type	trev
#151	closed	fixed	[Typed objects] Implement dynamically-sized array types	trev
#258	closed	fixed	[Typed objects] Implement a garbage collection mechanism	trev
#259	closed	rejected	[Typed objects] Implement forward declarations for types
#260	closed	fixed	[Typed objects] Implement type inheritance	trev
#393	closed	rejected	[Typed objects] Implement weak references
#505	closed	fixed	[Typed objects] Implement array helper methods	trev
#506	closed	rejected	[Typed objects] Guard against integer overflow issues
#507	closed	rejected	[Typed objects] Implement a light-weight array.slice() method	kzar
#510	closed	fixed	[Typed objects] Don't hardcode script load order in unit tests	trev
#517	closed	fixed	[Typed objects] Make unit tests compatible with Chrome and Safari	trev
#1772	closed	fixed	[JSHydra] Convert const to var for Chrome	trev
#1773	closed	fixed	[Typed objects] "assignment to undeclared variable bufferOffset" in unit tests	trev

[philll]

The assigned state will be dropped by #403

[fhd]

Since the Emscripten based approach is looking rather good, I'm not sure we really want to continue to work on Typed Objects. Makes it a P5.

[trev]

In fact, at that point I am certain that we are dropping typed objects and go with Emscripten instead. The performance issues we had with Emscripten initially are bound to affect us with typed objects as well (important points: static generation of JS bindings, stack-based allocations, likely more). Fixing these issues was already non-trivial with Emscripten, but with our own toolchain it will require far more effort - this isn't going to pay off if we have a reasonable and maintained alternative.