How can you check if an element belongs to one subtype or another?

问题

I just learnt about Enums and Types in Ada and decided to write a small program to practice:

with Ada.Text_IO;                       use Ada.Text_IO;
with Ada.Integer_Text_IO;       use Ada.Integer_Text_IO;

procedure Day is 

    type Day_Of_The_Week is (Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, Sunday);

    subtype Weekday is Day_Of_The_Week range Monday..Friday;

    subtype Weekend is Day_Of_The_Week range Saturday..Sunday;

        function is_Weekday ( dayOfTheWeek: in Day_Of_The_Week) return Boolean is
        begin
            if(--?--)
        end is_Weekday;

    selected_day_value  :   Integer;
    selected_day                :   Day_Of_The_Week;

begin
    Put_Line("Enter the number co-responding to the desired day of the week:");
    Put_Line("0 - Monday");
    Put_Line("1 - Tuesday");
    Put_Line("2 - Wednesday");
    Put_Line("3 - Thursday");
    Put_Line("4 - Friday");
    Put_Line("5 - Saturday");
    Put_Line("6 - Sunday");
    Get(selected_day_value);
    selected_day = Day_Of_The_Week'pos(selected_day_value);

    if( is_Weekday(selected_day))
        Put_Line( Day_Of_The_Week'Image(selected_day) & " is a weekday." );
    else
        Put_Line( Day_Of_The_Week'Image(selected_day) & " is a weekday." );

end Day;

I'm having trouble with the if statement. How can I check whether or not dayOfTheWeek is in the Weekday subtype or the weekend subtype?

回答1:

You want

function is_Weekday ( dayOfTheWeek: in Day_Of_The_Week) return Boolean is
begin
    return dayoFTheWeek in Weekday;
end is_Weekday;

Also, you want ’Val not ’Pos in

selected_day := Day_Of_The_Week'val(selected_day_value);

and you might take a look at the words in the second Put_Line!

回答2:

You don't need a function to check for this. In this case a function only obscures what happens:

if Selected_Day in Weekday then
  do stuff..
else
  do other stuff...
end if;

来源：https://stackoverflow.com/questions/9045646/how-can-you-check-if-an-element-belongs-to-one-subtype-or-another

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ada