Re: What is a byte?

["Dan'l Miller" <optikos@verizon.net>]

On Monday, July 28, 2014 2:48:16 PM UTC-5, Dan'l Miller wrote:
> On Monday, July 28, 2014 2:09:17 PM UTC-5, Victor Porton wrote:
> 
> > When I need to pass a byte to a C function, which Ada type should I use?

What you would *really* want to do in Ada is have a multistage Ada202X compiler that (at stage N) generates some Convention C code, then executes it to learn about the characteristics of the target C compiler, then generate the appropriate subtypes in corresponding stage-N+1 Ada source code, then compile that N+1 stage, where the app-domain Ada source-code is (i.e., where today's era of Ada source-code is).

Short of that state-of-the-art reflection (in e.g. multi-stage OCaml) to reflect the execution environment back into source code, the best that you can do is:
0) forego extreme portability entirely:  choose to support 8-bit bytes only with no Plan B and no apologies;
1) use a preprocessor (e.g., gnatprep; m4) to choose different Ada subtypes via conditional compilation;
2) use a child package for each different bit-size of byte:  one child package for 8-bit bytes, one child package for FPGAs' 9-bit bytes; and one child package for DSPs' 32-bit bytes;
3) use variant records or generics to force app-domain programmers to specify 8 or 9 or 32 in app-domain code
4) by far the worst of all:  evolve Ada202X to duplicate C++'s metatemplate-programming poor-man's functional-programming language to perform arcane contortions to achieve a limited amount of reflection with extremely-verbose syntax