[Gambas-user] Structure support in Gambas 3

[Benoît Minisini]

Hi,

I have just committed a new big internal change for Gambas 3 in revision 
#2970: structure support.

It is not 100% finished, must most of the useful parts are there. If that 
crashes your program - I will be amazed if it won't :-) - you know where to 
knock.

How does it work?

To define a structure, you must declare it inside a class or a module that 
way:

	Public Struct <StructName>
	  <Var1> As <Type1>
	  <Var2> As <Type2>
	End Struct

A structure is always public (at the moment).

A structure is a class, with only public members that are actually variables.

You can embed a structure inside an object that way:

	Private <ClassVariable> As Struct <StructName>

Note the 'Struct' keyword inserted before <StructName>.

An embedded structure is not an object on its own. Its data is allocated 
inside the object where it is declared. Like a "static array" (that should be 
named "embedded array" actually). Note that you cannot make an "embedded 
array" of static structures.

You can embed a structure inside another structure (logical, as a structure is 
a class). That way, you can create russian dolls if you like. Here is a stupid 
example:

	Public Struct Car
		Model As String
		Registration As String
		MaxSpeed As Float
	End Struct

	Public Struct Person
		Name As String
		Age As Integer
		BirthDate As Date
		FirstCar As Struct Car
		SecondCar As Struct Car
	End Struct

Passing structures to extern functions is not correctly supported at the 
moment, but it will.

That revision has another change: objects that do not raise events do not 
allocate an internal event management structure for nothing anymore. That 
saves 4 pointers (16 bytes on a 32 bits system) on each object, but I'm not 
100% sure I didn't do that misuse of memory ressources for nothing, so you may 
have a crash.

Now Fabien has just gb.report to finish, and I we will be able to release an 
alpha version of Gambas 3. :-)

But don't panic, there are a dozen of little things to do yet before the final 
release... The main thing are the package manager (I want it to be sure that 
it works correctly for the release, and I will need help for that), and the 
ability to release incremental versions of Gambas (3.1, 3.2...) that won't be 
just bug fixes like in the 2.x versions.

Enjoy it.

-- 
Benoît Minisini