Re: How to get Ada to “cross the chasm”?

[Jere <jhb.chat@gmail.com>]

On Wednesday, April 18, 2018 at 1:02:18 PM UTC-4, Lucretia wrote:
> On Wednesday, 18 April 2018 14:29:30 UTC+1, Jere  wrote:
> 
> > 1.  It favors static allocation over dynamic whenever possible.  This is
> > huge for small embedded systems.
> 
> So does Ada.
>  

This is an interesting point.  I would agree that programmers here at
comp.lang.ada promote avoiding access types whenever possible (Ada access 
types are more similar to pointers in the Rust world), but the Ada 
language itself doesn't really promote that.  It leaves the implementation 
of many aspects up to the compiler vendor.  Take, for example, discriminated 
records with a default discriminant.  The language standard doesn't direct 
how to implement that.  GNAT uses static allocation and throws an exception 
if you try to use a discriminant with very large range to create an array 
within the struct.  If I understand Randy's posts from other email chains, 
in Janus it can use the heap to allocate the array.  The secondary stack is 
another example.  It can be implemented as static only (I do this for my bare 
metal runtimes), heap, or a combination of both based on size (I think GNAT does
this normally?).  Ada's bounded containers are another example.  As far
as I can see in the standard, they don't require the use of static allocation
and can be heap implemented by the vendor.  The implementation advice
asks that they are implemented without heap, but it isn't binding (Which
makes them a portability nightmare for bare metal environments).  

NOTE:  That is my understanding based on emails here and what I have read in
the RM.  I apologize if I have misread.

I'm not saying this because I think Ada is bad (on the contrary, I prefer
Ada over Rust), but as a bare metal developer, Ada is frustratingly 
not specific on how memory is allocated by many basic language building 
blocks.  In the core Rust language, I know where the heap memory comes 
into play, so it is much easier to develop bare metal.