Feature request: Deploying a class instance in the default data segment

[Bill Baxter]

On Thu, Dec 18, 2008 at 2:05 PM, Weed <resume755 at mail.ru> wrote:
> Feature request: Deploying a class instance in the default data segment and
> creation of a class instance at compile time.
>
> In this post I'll try to prove the necessity of this feature.
>
> I have found that in D it is impossible to create a polymorphic object
> (class or struct) which can be created at compile-time.
>
> Good specific example of such an object is a matrix class.
>
> For some matrices it is good to create and initialize them at compile
> time, not dynamically at run time.
>
> Also for matrices of predefined size it is wrong to duplicate their
> dimensions (their width and height should be declared invariant and,
> consequently occupy memory only once)
>
> At the same time dynamically created matrices of arbitrary size which
> can be changed at run time are also needed. For example to make a slice of
> giant matrix it's more efficient to modify it in-place than to copy it.
> These matrices have variable width and height.
>
> So we have minimum two types of matrices: dynamic and constant sized with
> ability of compile time initialization. It is necessary to provide
> interaction between them (for example overload arithmetic operators
> for them). For this purpose it is necessary for them to be inherited
> from common parent.

This point I don't think is true.  DynamicMatrix can implement methods
like opMult(StaticMatrix M), and vice versa.

The only thing I can think of you can't do is make an array of
pointers to Matrix, the elements of which might be a DynamicMatrix, or
might be StaticMatrix.
But even that, if you really feel you need it for some reason, could
be done using a struct/class with a union inside.  Most cases where
you might want to accept either/or can be done with templates.

> So it can not be structures, only classes.
>
> But classes can not be created at compile time.
>
> So I propose to add possibility of deployment of class instance in the
> default data segment and creation of class instance at compile time.

This might be a useful feature, but I'm not finding your argument for
it quite convincing enough yet.

--bb