Ada. Why is <<procedurename.all>> required to call a procedure from a pointer?

Question

I am very new to Ada, and I am wondering why I have to write Acc.all, or d.all to call the procedures through the pointers. I thought .all was mainly for Records, because then you could set .all record values equal to some other record value. At the same time I am wondering why I am not required to do so when I am calling the function. Here is my code for reference. Please forget about AnimalPKG.Animals(Total, 3,2,1), as I am just practicing how to import packages.

    with AnimalPKG, Ada.Text_IO, Ada.Integer_Text_IO; 
    use Ada.Text_IO, Ada.Integer_Text_IO; 

    procedure Main is

       procedure thisisaccess is
          begin
          Put("thisisaccess"); 

          end thisisaccess;

       Type accessprocedure is access procedure;

       procedure passinfunction(d : accessprocedure) is 
          begin
         d.all; 
       end passinfunction; 

       function times5(a : Integer) return Integer is 
          begin
          return a*5; 
       end times5; 

       Type times5access is access function(x : Integer) return Integer; 

       B : times5access := times5'Access; 

        Acc : accessprocedure;
       Acc2 : accessprocedure;  //Modification

   Total : Integer;


begin

   Acc := thisisaccess'Access; //Modification
   Acc2 := Acc; //Modification
   Acc2.all; //Modification

       AnimalPKG.Animals(Total, 3,2,1); 
       Put(Total); 
       Acc.all; 
       passinfunction(Acc); 
       Put(B(3)); 
    end Main;

Ondrej Tucny Ondrej Tucny · Accepted Answer · 2016-12-01T14:20:48

The .all construct is an explicit dereference. The compiler can't otherwise tell if by P, which is of an access procedure type, you mean the pointer itself, or a call. Note that in Ada empty parenthesis are not required when invoking a procedure. Hence P is understood as the pointer itself, and P.all as a call.

Ada. Why is <<procedurename.all>> required to call a procedure from a pointer?

1 Answers