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11.3 Raise Statements

[A raise_statement raises an exception.] 


{AI95-00361-01} raise_statement ::= raise;
      | raise exception_name [with string_expression];
 raise [exception_name];

Legality Rules

The name, if any, in a raise_statement shall denote an exception. {re-raise statement} A raise_statement with no exception_name (that is, a re-raise statement) shall be within a handler, but not within a body enclosed by that handler. 

Name Resolution Rules

  {AI95-00361-01} The expression, if any, in a raise_statement, is expected to be of type String. 

Dynamic Semantics

{AI95-00361-01} {raise (an exception)} To raise an exception is to raise a new occurrence of that exception[, as explained in 11.4]. {execution (raise_statement with an exception_name) [partial]} For the execution of a raise_statement with an exception_name, the named exception is raised. [If a string_expression is present, the expression is evaluated and its value is associated with the exception occurrence.] {execution (re-raise statement) [partial]} For the execution of a re-raise statement, the exception occurrence that caused transfer of control to the innermost enclosing handler is raised [again]. 
Proof: {AI95-00361-01} The definition of Exceptions.Exception_Message includes a statement that the string is returned (see 11.4.1). We describe the use of the string here so that we don't have an unexplained parameter in this subclause. 
Implementation Note: For a re-raise statement, the implementation does not create a new Exception_Occurrence, but instead propagates the same Exception_Occurrence value. This allows the original cause of the exception to be determined. 


Examples of raise statements: 
{AI95-00433-01} raise Ada.IO_Exceptions.Name_Error;   -- see A.13
raise Queue_Error with "Buffer Full"; -- see 9.11
raise;                                -- re-raise the current exception

Wording Changes from Ada 83

The fact that the name in a raise_statement has to denote an exception is not clear from RM83. Clearly that was the intent, since the italicized part of the syntax rules so indicate, but there was no explicit rule. RM83-1.5(11) doesn't seem to give the italicized parts of the syntax any force. 

Extensions to Ada 95

{AI95-00361-01} {extensions to Ada 95} The syntax of a raise_statement is extended to include a string message. This is more convenient than calling Exceptions.Exception_Message (exception_name'Identity, string_expression), and should encourage the use of message strings when raising exceptions.

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