12.2 Generic Bodies

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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.

Dynamic Semantics

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

4 The syntax of generic subprograms implies that a generic subprogram body is always the completion of a declaration.

Examples

Example of a generic procedure body:

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;

Example of a generic function body:

function Squaring(X : Item) return Item is  --  see 12.1
begin
    return X*X;  --  the formal operator "*"
end Squaring;

Example of a generic package body:

package body On_Vectors is  --  see 12.1

    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;

        for N in A'Range loop 
            Result(N) := Sum(A(N), B(N + Bias)); -- the formal function Sum    
        end loop;
        return Result;
    end Sum;

    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;

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