Datatype of variable in ada

Question

How can I find the datatype of a variable in Ada?

For example, given

INT : integer;

how can I print "the datatype is integer" for this variable?

In Python, type() can be used to find the type. Is there any similar function in Ada to find the datatype of a variable?

score 5 · Accepted Answer · answered Apr 02 '15 at 06:39

5

Ada is a strongly typed language, and when you declare a variable you specify its type. So there is no use for a function to return the variable's type, as there would be in languages with untyped variables. The program already knows the type.

If a variable X is declared with type T'Class, then the type of the actual value can be T or any type derived from T. In that case, you can use X'Tag to get the tag of the value's actual type, which is the closest you can come to getting the actual type. Once you have a tag, you can do things like getting the type's name (there are functions for this in Ada.Tags), comparing it to the tag of some type to see if it's that type, etc. But Integer is not a tagged type, so you can't use 'Tag on it and there would be no use for it.

answered Apr 02 '15 at 06:39

ajb

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You can also check `Classwide_Instance in Derived_Type’Class` to see whether the instance is of type `Derived_Type` (or of one of its derived types, of course, if there are any). – Simon Wright Jan 16 '16 at 22:03
"As there would be in languages with untyped variables." C# is considered to be a strongly typed language, yet you can use "is" operator to test if an object is of a certain type and typeof() to get its type. This vary useful when using polymorphic types. Let's say you have a bunch of, say Shape objects, and you want to determine whether if they are squares, circles or triangles. Without it, you have to assign a explicit "kind" to the objects. – ATL_DEV May 30 '22 at 01:05

score 0 · Answer 2 · answered Apr 06 '15 at 11:42

If you declare INT as a Integer, it will always be a Integer in that scope. So you could just make a function like:

function the_type(I : Integer) return String is ("Integer");

I can't think of a reason you would want to check the type of variable INT if it always going to be a Integer.

On the other hand if INT can change type at run-time you will need code to emulate that:

procedure Main is
    type Memory_Type_Enum is (Integer_Type, Float_Type);

    record Variable
        Memory_Location : Address;
        Memory_Type : Memory_Type_Enum;
    end record;

    INT : Variable;
begin
    INT := Allocate_Variable(Float_Type);
    INT := Allocate_Variable(Integer_Type);
    Put_Line(INT.Memory_Type'Img);
end;

But it's up to you how you implement a type check whether you have dynamic type system or static.

Datatype of variable in ada

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