Array Sorting
Author: JTC1/SC22/WG9/ARG, by Randall Brukardt, ARG Editor

Ada Reference Manual — Legal Information

# A.18.16 Array Sorting

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The language-defined generic procedures Containers.Generic_Array_Sort and Containers.Generic_Constrained_Array_Sort provide sorting on arbitrary array types.

#### Static Semantics

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The generic library procedure Containers.Generic_Array_Sort has the following declaration:
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generic
type Index_Type is (<>);
type Element_Type is private;
type Array_Type is array (Index_Type range <>) of Element_Type;
with function "<" (Left, Right : Element_Type)
return Boolean is <>;
procedure Ada.Containers.Generic_Array_Sort (Container : in out Array_Type);
pragma Pure(Ada.Containers.Generic_Array_Sort);
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Reorders the elements of Container such that the elements are sorted smallest first as determined by the generic formal "<" operator provided. Any exception raised during evaluation of "<" is propagated.
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The actual function for the generic formal function "<" of Generic_Array_Sort is expected to return the same value each time it is called with a particular pair of element values. It should define a strict ordering relationship, that is, be irreflexive, asymmetric, and transitive; it should not modify Container. If the actual for "<" behaves in some other manner, the behavior of the instance of Generic_Array_Sort is unspecified. How many times Generic_Array_Sort calls "<" is unspecified.
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The generic library procedure Containers.Generic_Constrained_Array_Sort has the following declaration:
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generic
type Index_Type is (<>);
type Element_Type is private;
type Array_Type is array (Index_Type) of Element_Type;
with function "<" (Left, Right : Element_Type)
return Boolean is <>;
procedure Ada.Containers.Generic_Constrained_Array_Sort
(Container : in out Array_Type);
pragma Pure(Ada.Containers.Generic_Constrained_Array_Sort);
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Reorders the elements of Container such that the elements are sorted smallest first as determined by the generic formal "<" operator provided. Any exception raised during evaluation of "<" is propagated.
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The actual function for the generic formal function "<" of Generic_Constrained_Array_Sort is expected to return the same value each time it is called with a particular pair of element values. It should define a strict ordering relationship, that is, be irreflexive, asymmetric, and transitive; it should not modify Container. If the actual for "<" behaves in some other manner, the behavior of the instance of Generic_Constrained_Array_Sort is unspecified. How many times Generic_Constrained_Array_Sort calls "<" is unspecified.

#### Implementation Advice

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The worst-case time complexity of a call on an instance of Containers.Generic_Array_Sort or Containers.Generic_Constrained_Array_Sort should be O(N**2) or better, and the average time complexity should be better than O(N**2), where N is the length of the Container parameter.
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Containers.Generic_Array_Sort and Containers.Generic_Constrained_Array_Sort should minimize copying of elements.

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