11.1 Exception Declarations
Reason: We considered removing this requirement
inside generic bodies, because it is an implementation burden for implementations
that wish to share code among several instances. In the end, it was decided
that it would introduce too much implementation dependence.
Hence, if an exception_declaration
occurs in a recursive subprogram, the exception name denotes the same
exception for all invocations of the recursive subprogram. The reason
for this rule is that we allow an exception occurrence to propagate out
of its declaration's innermost containing master; if exceptions were
created by their declarations like other entities, they would presumably
be destroyed upon leaving the master; we would have to do something special
to prevent them from propagating to places where they no longer exist.
Ramification: Exception identities are
unique across all partitions of a program.
exceptions are the ones declared in the declaration
of package Standard: Constraint_Error, Program_Error, Storage_Error,
and Tasking_Error[; one of them is raised when a language-defined check
Ramification: The exceptions declared
in the language-defined package IO_Exceptions, for example, are not predefined.
execution of any construct raises Storage_Error if there is insufficient
storage for that execution.
The amount of storage
needed for the execution of constructs is unspecified.
Ramification: Note that any execution
whatsoever can raise Storage_Error. This allows much implementation freedom
in storage management.
Examples of user-defined
Singular : exception;
Error : exception;
Overflow, Underflow : exception;
Inconsistencies With Ada 83
The exception Numeric_Error
is now defined in the Obsolescent features Annex, as a rename of Constraint_Error.
All checks that raise Numeric_Error in Ada 83 instead raise Constraint_Error
in Ada 95. To increase upward compatibility, we also changed the rules
to allow the same exception to be named more than once by a given handler.
Constraint_Error | Numeric_Error =>”
will remain legal in Ada 95, even though Constraint_Error and Numeric_Error
now denote the same exception. However, it will not be legal to have
separate handlers for Constraint_Error and Numeric_Error. This change
is inconsistent in the rare case that an existing program explicitly
raises Numeric_Error at a point where there is a handler for Constraint_Error;
the exception will now be caught by that handler.
Wording Changes from Ada 83
Extensions to Ada 2005
Ada 2005 and 2012 Editions sponsored in part by Ada-Europe