Ada Reference Manual (Ada 2022) — Legal Information

# 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

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

#### Examples

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Example of a generic procedure body:
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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;
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Example of a generic function body:
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function Squaring(X : Item) return Item is -- see 12.1
begin
return X*X; -- the formal operator "*"
end Squaring;
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Example of a generic package body:
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package body On_Vectors is -- see 12.1
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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;
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for N in A'Range loop
Result(N) := Sum(A(N), B(N + Bias)); -- the formal function Sum
end loop;
return Result;
end Sum;
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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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