C language extension - Automatically cast

C language extension - Automatically cast

[Sławomir Lach]

In desperation made by programming in GTK+ I realized, some of object 
languages could been implemented in C, but only these not require to made 
changes in programs in runtime (compiler output).

One of items is automatically cast. For example I declared variable called 
Button of GtkButton and pass it to function requires GtkWidget. Why do not 
automatically cast to GtkWidget (like in class hierarchy or conversion 
operator in C++ or some extra constructors)? But .. it's rather conversion 
operator.

It could looks like:
__gcc_parent_type GtkWidget __gcc_parent_type_for GtkButton, GtkLabel, 
GtkTextView
__gcc_parent_type GtkBin __gcc_parent_type_for GtkWindow, GtkBox

What do you think?

It makes sense, because in this case there's no way to made mistake by 
avoiding extra conversion. Function expected any of GtkWidget (for example), 
so passing GtkButton is good. Code would be cleaner, hands will be in better 
shape and we save programmers time.

Re: C language extension - Automatically cast

[Florian Weimer]

* Sławomir Lach:

> One of items is automatically cast. For example I declared variable called 
> Button of GtkButton and pass it to function requires GtkWidget. Why do not 
> automatically cast to GtkWidget (like in class hierarchy or conversion 
> operator in C++ or some extra constructors)? But .. it's rather conversion 
> operator.
>
> It could looks like:
> __gcc_parent_type GtkWidget __gcc_parent_type_for GtkButton, GtkLabel, 
> GtkTextView
> __gcc_parent_type GtkBin __gcc_parent_type_for GtkWindow, GtkBox
>
> What do you think?

-fplan9-extensions already implements support for something like this.

But for portable code in that style, you should probably use C++
instead.

Thanks,
Florian