- 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
case expression is
when discrete_choice_list =>
Name Resolution Rules
- The expression is expected to be of any discrete type. The expected type
for each discrete_choice is the type of the expression.
- 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.
- The possible values of the expression shall be covered as follows:
- If the expression is a name (including a type_conversion or a
function_call) having a static and constrained nominal subtype,
or is a qualified_expression whose subtype_mark denotes a static
and constrained scalar subtype, then each non-others discrete_choice shall cover only values in that subtype, and each value of
that subtype shall be covered by some discrete_choice (either
explicitly or by others).
- If the type of the expression is root_integer, universal_integer,
or a descendant of a formal scalar type, then the case_statement
shall have an others discrete_choice.
- Otherwise, each value of the base range of the type of the
expression shall be covered (either explicitly or by others).
- Two distinct discrete_choices of a case_statement shall not cover the
- For the execution of a case_statement the expression is first evaluated.
- If the value of the expression is covered by the discrete_choice_list of
some case_statement_alternative, then the sequence_of_statements of the
_alternative is executed.
- Otherwise (the value is not covered by any discrete_choice_list, perhaps
due to being outside the base range), Constraint_Error is raised.
(5) 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.
- Examples of case statements:
case Sensor is
when Elevation => Record_Elevation(Sensor_Value);
when Azimuth => Record_Azimuth (Sensor_Value);
when Distance => Record_Distance (Sensor_Value);
when others => null;
case Today is
when Mon => Compute_Initial_Balance;
when Fri => Compute_Closing_Balance;
when Tue .. Thu => Generate_Report(Today);
when Sat .. Sun => null;
case Bin_Number(Count) is
when 1 => Update_Bin(1);
when 2 => Update_Bin(2);
when 3 | 4 =>
when others => raise Error;
-- Email comments, additions, corrections, gripes, kudos, etc. to:
Magnus Kempe -- Magnus.Kempe@di.epfl.ch
Page last generated: 95-03-12