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arraysadaassign

Copy arrays of same type and size but different index type in Ada

I am learning Ada at the moment and the current lesson is on arrays. Consider the following program;

procedure Main is
   type T_Bool is array (Boolean) of Integer;
   type T_Intg is array (Integer range 1 .. 2) of Integer;
   A1 : T_Bool := (others => 0);
   A2 : T_Intg := (others => 0);
begin
   -- None of these statements work
   A2 := A1;
   A2 (1 .. 2) := A1 (false .. true);
   A2 := A1 (Boolean'First .. Boolean'Last);
end Main;

According to the Adacore university tutor, it is possible to copy values from one array to another as long as the lengths are the same. In the code snippet, why can you not assign arrays with the same size but different indexing methods, despite the fact that the length is the same?

What is the correct way to copy this across? Is it a case of looping through all indexes in the Boolean type range and copying the corresponding array index across or is there another clever way of doing it?

Solution

  • The tutorial says, on slide 3, that "all arrays are (doubly) typed", which means that - as usual for different types - you can't assign between your two array types; so yes, you need a loop.

    There are "clever" ways using, for example, unchecked conversion; but, really, don't go there!