- The following language-defined library package exists:
package Ada.Exceptions is
type Exception_Id is private;
Null_Id : constant Exception_Id;
function Exception_Name(Id : Exception_Id) return String;
type Exception_Occurrence is limited private;
type Exception_Occurrence_Access is access all Exception_Occurrence;
Null_Occurrence : constant Exception_Occurrence;
procedure Raise_Exception(E : in Exception_Id; Message : in String := "");
function Exception_Message(X : Exception_Occurrence) return String;
procedure Reraise_Occurrence(X : in Exception_Occurrence);
function Exception_Identity(X : Exception_Occurrence) return Exception_Id;
function Exception_Name(X : Exception_Occurrence) return String;
-- Same as Exception_Name(Exception_Identity(X)).
function Exception_Information(X : Exception_Occurrence) return String;
procedure Save_Occurrence(Target : out Exception_Occurrence;
Source : in Exception_Occurrence);
function Save_Occurrence(Source : Exception_Occurrence)
... -- not specified by the language
- Each distinct exception is represented by a distinct value of type
Exception_Id. Null_Id does not represent any exception, and is the default
initial value of type Exception_Id. Each occurrence of an exception is
represented by a value of type Exception_Occurrence. Null_Occurrence does
not represent any exception occurrence, and is the default initial value of
- For a prefix E that denotes an exception, the following attribute is
E'Identity returns the unique identity of the exception. The
type of this attribute is Exception_Id.
- Raise_Exception raises a new occurrence of the identified exception. In
this case, Exception_Message returns the Message parameter of Raise_Exception. For a raise_statement with an exception_name, Exception_Message
returns implementation-defined information about the exception occurrence.
Reraise_Occurrence reraises the specified exception occurrence.
- Exception_Identity returns the identity of the exception of the
- The Exception_Name functions return the full expanded name of the
exception, in upper case, starting with a root library unit. For an
exception declared immediately within package Standard, the defining_identifier is returned. The result is implementation defined if the
exception is declared within an unnamed block_statement.
- Exception_Information returns implementation-defined information about
the exception occurrence.
- Raise_Exception and Reraise_Occurrence have no effect in the case of
Null_Id or Null_Occurrence. Exception_Message, Exception_Identity,
Exception_Name, and Exception_Information raise Constraint_Error for a
Null_Id or Null_Occurrence.
- The Save_Occurrence procedure copies the Source to the Target. The
Save_Occurrence function uses an allocator of type Exception_Occurrence_Access to create a new object, copies the Source to this new object, and
returns an access value designating this new object; the result may be
deallocated using an instance of Unchecked_Deallocation.
- The implementation of the Write attribute (see 13.13.2)
of Exception_Occurrence shall support writing a representation of an exception
occurrence to a stream; the implementation of the Read attribute of Exception_Occurrence
shall support reconstructing an exception occurrence from a stream (including
one written in a different partition).
- An implementation of Exception_Name in a space-constrained environment
may return the defining_identifier instead of the full expanded name.
- The string returned by Exception_Message may be truncated (to no less
than 200 characters) by the Save_Occurrence procedure (not the function), the
Reraise_Occurrence procedure, and the re-raise statement.
- Exception_Message (by default) and Exception_Information should produce
information useful for debugging. Exception_Message should be short (about
one line), whereas Exception_Information can be long. Exception_Message
should not include the Exception_Name. Exception_Information should include
both the Exception_Name and the Exception_Message.
-- Email comments, additions, corrections, gripes, kudos, etc. to:
Magnus Kempe -- Magnus.Kempe@di.epfl.ch
Page last generated: 95-03-12