Overview of Ada 2022
Chapter 1: Introduction
Let us begin with why do we need another revision,
when Ada has been used to successfully deliver so many projects around
the world, indeed across the solar system?
The world has moved on. The most significant external
factor has probably been the growth of the number of cores on a processor.
Making use of the first multi-core processors was relatively easy for
Ada compared with other languages as tasking had been included from the
outset. Maybe latent timing problems would emerge when tasks were truly
running on different processors instead of just pretending to, but these
problems were small scale compared with, say, elaboration order problems
when moving between different vendors' compilers.
These days a processor may have dozens of cores,
maybe in the future it will be hundreds. Thus the first improvement given
in the list of instructions (see below) from WG 9 (the ISO/IEC Working
Group responsible for Ada), to the Ada Rapporteur Group (ARG), was finer
grained control of parallelism.
The ARG follows the following instructions from WG
9, extracted from ISO/IEC JTC 1/SC 22/WG 9 N571:
“The ARG is
requested to pay particular attention to the following two categories
Improvements that will maintain or improve Ada's advantages, especially
in those user domains where safety and security are prime concerns;
Improvements that will remedy shortcomings in Ada.
special interest in these categories are:
Improving the capabilities of Ada on multi-core
and multi-threaded architectures;
Improving the ability to write and enforce
contracts for Ada entities (for instance, via preconditions);
Improving the use and functionality of
the predefined containers;
Improving support for Unicode in the language
and predefined libraries.
These are all examples of improvements in category
A, except for the last which is an example of an improvement in category
New real-time features have also arisen, primarily
from recommendations from the series of International Real-Time Ada Workshops
As always, there is the balancing act to be struck
between keeping the language stable and backwardly compatible, and adding
new features to keep with the times.
Each topic is organized in terms of the relevant
Ada Issue(s). When appropriate, a reference to the Reference Manual subclause
that primarily defines the feature is also included.
An Ada Issue is an investigation of a comment raised
on the Ada standard. These are first worked on and approved by the ARG.
They are then passed to WG 9 for consideration and approval before eventually
being consolidated and sent to ISO for formal processing to create a
revised internation standard. Ada Issues raised on Ada 2012 were assigned
numbers of the form AI12-nnnn-aa, where aa is the alternative number.
These AIs may be found at http://www.ada-auth.org/AI12-SUMMARY.HTML
(for HTML versions of this document, the numbers link to the appropriate
AI as well). The relevant AI title and number are quoted in the following
sections, omitting the alternative number if there is only one alternative.
Thanks to Randy Brukardt for his many suggestions,
and to John Barnes for his review comments, and to the rest of the ARG,
especially Tucker Taft, for their examples.
NOTE 1 Contemporary English is used
where possible, but where a word is quoted from the RM, then of necessity
the US spelling is used.
NOTE 2 RM references give the location
of the primary definition of a features; rules defining the feature may
occur in other parts of the RM as well. An RM reference is not given
when a feature does not have a obvious primary definition; the feature
may be defined in multiple places or implicitly in rules defining other
© 2021, 2022 Jeff Cousins