12.2 Generic Bodies

1
The body of a generic unit (a generic body) [is a template for the instance bodies. The syntax of a generic body is identical to that of a nongeneric body].
1.a
Ramification: We also use terms like “generic function body” and “nongeneric package body.”

Dynamic Semantics

2
The elaboration of a generic body has no other effect than to establish that the generic unit can from then on be instantiated without failing the Elaboration_Check. If the generic body is a child of a generic package, then its elaboration establishes that each corresponding declaration nested in an instance of the parent (see 10.1.1) can from then on be instantiated without failing the Elaboration_Check.
NOTES
3
4  The syntax of generic subprograms implies that a generic subprogram body is always the completion of a declaration.

Examples

4
Example of a generic procedure body:
5
procedure Exchange(U, V : in out Elem) is  -- see 12.1
T : Elem;  --  the generic formal type
begin
T := U;
U := V;
V := T;
end Exchange;
6
Example of a generic function body:
7
function Squaring(X : Item) return Item is  --  see 12.1
begin
return X*X;  --  the formal operator "*"
end Squaring;
8
Example of a generic package body:
9
package body On_Vectors is  --  see 12.1
10
function Sum(A, B : Vector) return Vector is
Result : Vector(A'Range); --  the formal type Vector
Bias   : constant Integer := B'First - A'First;
begin
if A'Length /= B'Length then
raise Length_Error;
end if;
11
for N in A'Range loop
Result(N) := Sum(A(N), B(N + Bias)); -- the formal function Sum
end loop;
return Result;
end Sum;
12
function Sigma(A : Vector) return Item is
Total : Item := A(A'First); --  the formal type Item
begin
for N in A'First + 1 .. A'Last loop
Total := Sum(Total, A(N)); --  the formal function Sum
end loop;
return Total;
end Sigma;
end On_Vectors; Ada 2005 and 2012 Editions sponsored in part by Ada-Europe