Section 11: Exceptions
1
[This section defines the facilities for dealing
with errors or other exceptional situations that arise during program
execution.]
{exception occurrence}
{condition: See also
exception} {signal
(an exception): See raise} {throw
(an exception): See raise} {catch
(an exception): See handle} {Exception}
[Glossary Entry]
An
exception represents a
kind of exceptional situation; an occurrence of such a situation (at
run time) is called an
exception occurrence. [
{raise
(an exception) [partial]} To
raise
an exception is to abandon normal program execution so as to draw attention
to the fact that the corresponding situation has arisen.
{handle
(an exception) [partial]} Performing some
actions in response to the arising of an exception is called
handling
the exception. ]
1.a
To be honest: {
handle (an exception
occurrence) [partial]}
...or handling the exception
occurrence.
1.b
Ramification: For example, an exception
End_Error might represent error situations in which an attempt is made
to read beyond end-of-file. During the execution of a partition, there
might be numerous occurrences of this exception.
1.c
To be honest: {
occurrence (of an exception)}
When the meaning is clear from the context, we sometimes
use “
occurrence” as a short-hand for “exception
occurrence.”
2
[An exception_declaration
declares a name for an exception. An exception is raised initially either
by a raise_statement or by the failure of
a language-defined check. When an exception arises, control can be transferred
to a user-provided exception_handler at the
end of a handled_sequence_of_statements, or
it can be propagated to a dynamically enclosing execution.]
Wording Changes from Ada 83
2.a
We are more explicit about the difference between
an exception and an occurrence of an exception. This is necessary because
we now have a type (Exception_Occurrence) that represents exception occurrences,
so the program can manipulate them. Furthermore, we say that when an
exception is propagated, it is the same occurrence that is being propagated
(as opposed to a new occurrence of the same exception). The same issue
applies to a re-raise statement. In order to understand these semantics,
we have to make this distinction.
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