1
A case_statement selects for execution one of a number of alternative sequences_of_statements; the chosen alternative is defined by the value of an expression.
2
case_statement::=
case expression is
case_statement_alternative
{case_statement_alternative}
end case;
3
case_statement_alternative::=
when discrete_choice_list =>
sequence_of_statements
4
The expression is expected to be of any discrete type. The expected type for each discrete_choice is the type of the expression.
5
The expressions and discrete_ranges given as discrete_choices of a case_statement shall be static. A discrete_choice others, if present, shall appear alone and in the last discrete_choice_list.
6
The possible values of the expression shall be covered as follows:
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8
9
10
Two distinct discrete_choices of a case_statement shall not cover the same value.
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For the execution of a case_statement the expression is first evaluated.
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If the value of the expression is covered by the discrete_choice_list (see 3.8.1) of some case_statement_alternative (see 5.4), then the sequence_of_statements (see 5.1) of the _alternative is executed.
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Otherwise (the value is not covered by any discrete_choice_list, perhaps due to being outside the base range), Constraint_Error is raised.
NOTES
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4 The execution of a case_statement chooses one and only one alternative. Qualification of the expression of a case_statement by a static subtype can often be used to limit the number of choices that need be given explicitly.
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Examples of case statements:
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case Sensor is when Elevation => Record_Elevation(Sensor_Value); when Azimuth => Record_Azimuth (Sensor_Value); when Distance => Record_Distance (Sensor_Value); when others => null; end case;
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case Today is when Mon => Compute_Initial_Balance; when Fri => Compute_Closing_Balance; when Tue .. Thu => Generate_Report(Today); when Sat .. Sun => null; end case;
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case Bin_Number(Count) is when 1 => Update_Bin(1); when 2 => Update_Bin(2); when 3 | 4 => Empty_Bin(1); Empty_Bin(2); when others => raise Error; end case;