Mantis 1345

P1800-2008/D4

12.5, unique case

In Section 12.5

CHANGE

In a unique-case, it shall be legal to evaluate a case item expression at any time after the evaluation of the case expression and before the evaluation of the corresponding comparison. A unique-case shall be illegal if, for any such interleaving of evaluations and comparisons, more than one case item matches the case expression. For an illegal unique-case, an implementation shall be required to issue a warning message, unless it can demonstrate a legal interleaving of evaluations and comparisons so that no more than one case item matches the case expression. To implement this requirement, an implementation can continue the evaluations and comparisons after the termination of the usual linear search and before the execution of the statement associated with the first matching case item. However, the statements associated with any additional matching case items shall not be executed.

TO (This will supercede the changes in Mantis 1041 to this paragraph)

In a unique-case, it shall be legal to evaluate a case item expression at any time after the evaluation of the case expression and before the evaluation of the corresponding comparison. A unique-case shall be illegal if, for any such interleaving of evaluations and comparisons, more than one case item matches the case expression. For an illegal unique-case, an implementation shall be required to issue a warning message, unless it can demonstrate a legal interleaving of evaluations and comparisons so that no more than one case item matches the case expression. To implement this requirement, an implementation can continue the evaluations and comparisons after the termination of the usual linear search and before the execution of the statement associated with the first matching case item. However, the statements associated with any additional matching case items shall not be executed.

In a unique-case, the case_expression shall be evaluated exactly once and before any of the case_item expressions. The case_item expressions may be evaluated in any order and compared in any order. A unique-case is violated if more than one case_item is found to match the case_expression and the implementation shall issue a warning. The implementation shall continue the evaluations and comparisons after finding the first matching case_item and before the execution of the statement associated with that case_item but the statements associated with additional matching case_items shall not be executed. After finding a uniqueness violation, the tool implementation is not required to continue evaluating and comparing additional case_items. An implementation is not required to try more than one order of evaluations and comparisons of case_item expressions. The presence of side-effects in the case_item expressions may cause non-deterministic results. It is not a violation of uniqueness for a single case_item to contain more than one case_item expression that matches the case_expression. If a case_item expression matches the case_expression, the implementation is not required to evaluate additional case_item expressions in the same case_item.