Re: some questions re. Ada/GNAT from a C++/GCC user

[Mike Young <mikey@mcs.com>]

John G. Volan wrote:
> 
> One difficulty I see with intermingling declarations and statements is
> how to interpret declarations within conditional or iterative constructs.
> For instance:
> 
>     -- This is NOT Ada, this is CRAPOLA (C-Reminiscent Ada-like Perversion
>     -- Of Language Aspects)  :-) :
>     begin
>         ...
>         if Smaller then
>             X : Integer;
>             ...
>         elsif Bigger then
>             X : Long_Integer;
>             ...
>         end if;
>         ...
>         -- is X in scope here, and if so, what the heck is it?
>         ...

==========
(Cute acronym; not sure if I like it though. :)

The scoping rules in C++ are quite simple: the object comes into 
existence at the point of definition, and persists until the end of the 
enclosing scope. In your example, X would is created at its declaration 
(eg.: X : Long_Integer;), and is destroyed at the corresponding elsif or 
endif.

Sprinkling declarations willy-nilly throughout the code is more than a 
matter of convenience. Construction of objects sometimes entail 
non-trivial construction. Rather than force a two step process -- 
construction at declaration, and then subsequent initialization -- it is 
very common to declare the object "just-in-time," and combine the two 
steps. This frees the object designer from allowing for an undefined 
state, which would exist if construction were separated from 
initialization.

Personally, I like it this way. It's very easy to verify that all 
objects are correctly initialized before use when all objects are 
initialized at their points of construction. The object does not exist 
before it is initialized.

Mike.