ada

Does Ada have a type equivalent to Pascal's set?


I'm learning Ada as a spare-time activity and, while I realise that it is greatly inspired by Pascal, I can't find a type that is similar to Pascal's set.

set is built into the Pascal language itself and uses one bit per element. So, for example, var a: set of char; declares a (typically) 256-bit data type that can hold any set of characters.

In Ada, I can see that it has sets as part of its library (not a built-in language feature) but those are more like Java's HashSet or C++'s unordered_set and take up much more memory than 1 bit per element. Am I missing something?


Solution

  • You can use a Boolean array to get an equivalent type:

    type Element is (A, B, C, D);
    -- The possible elements of the sets.
    
    type Set is array (Element) of Boolean;
    -- A set of Elements. An Element E is in the
    -- set S if and only if S(E) is True.
    
    B_and_D : Set := (B | D => True, others => False);
    --  A set initialized to contain B and D.
    

    If you want to store the elements in single bits, add "with Pack" to the declaration of type Set. For example, if you want a set of Characters, using 256 bits, that would be

    type Char_Set is array (Character) of Boolean
    with Pack;