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TArrayUtils-DeleteAndFreeRange.md

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DeleteAndFreeRange<T: class> class method

Project: Array Utilities Unit

Unit: DelphiDabbler.Lib.ArrayUtils

Record: TArrayUtils

Applies to: ~>0.1

class procedure DeleteAndFreeRange<T: class>(var A: TArray<T>;
  AStartIndex, AEndIndex: Integer);
  overload; static;

class procedure DeleteAndFreeRange<T: class>(var A: TArray<T>;
  AStartIndex: Integer);
  overload; static;

Description

Deletes and frees a range of one or more elements of from an array of TObject descendant objects.

The length of the array is reduced by the number of elements deleted.

Parameters:

  • A - Array from which the elements are to be deleted and freed. The array is updated in place. Empty arrays are ignored.

    Array elements must be TObject descendants.

  • AStartIndex - Index of the first element in the range to be deleted and freed.

    If AStartIndex < 0 then it is adjusted to be equal to 0.

  • AEndIndex - Optional parameter containing the index of the last element in the range to be deleted and freed.

    If AEndIndex is not supplied then the end of the range is assumed to be the last element of the array, so that all elements from AStartIndex to the end of the array are deleted and freed.

    If AEndIndex is ≥ Length(A) then it is adjusted to be equal to Length(A) - 1.

    If AEndIndex < AStartIndex, after both have been adjusted, then no elements are deleted and A is not changed.

Notes

If you want to delete and free all the elements of an array with indices ≥ AStartIndex then there is no need to provide AEndIndex.

To delete and free a single element set both AStartIndex and AEndIndex to the same index. Alternatively use DeleteAndFree<T: class>.

Example

Both examples below use a custom TObjectEx class that records the number of objects currently instantiated. This is defined as follows:

type
  TObjectEx = class
  public
    var ID: Char;
    class var InstanceCount: Integer;
    constructor Create(AID: Char);
    destructor Destroy; override;
  end;

{ TObjectEx }

constructor TObjectEx.Create(AID: Char);
begin
  inherited Create;
  ID := AID;
  Inc(InstanceCount);
end;

destructor TObjectEx.Destroy;
begin
  Dec(InstanceCount);
  inherited;
end;

Example #1

This first example uses the overload of DeleteAndFreeRange<T: class> that takes both the start and end indices of a range as parameters.

procedure DeleteAndFreeRange_Eg1;
var
  A: TArray<TObjectEx>;
  Obj: TObjectEx;
  Constraint: TArrayUtils.TConstraint<TObjectEx>;
begin
  // Start with no objects
  Assert(TObjectEx.InstanceCount = 0, 'TObjectEx <> 0 instances');

  // Create array of 6 objects
  A := TArray<TObjectEx>.Create(
    TObjectEx.Create('A'), TObjectEx.Create('B'),
    TObjectEx.Create('C'), TObjectEx.Create('D'),
    TObjectEx.Create('E'), TObjectEx.Create('F')
  );
  Assert(Length(A) = 6, 'Array length <> 6');
  Assert(TObjectEx.InstanceCount = 6, 'TObjectEx <> 4 instances');
  Assert(A[2].ID = 'C', 'A[2] <> C');
  Assert(A[3].ID = 'D', 'A[3] <> D');
  Assert(A[4].ID = 'E', 'A[4] <> E');

  // Delete and free all objects in range [2..4]
  TArrayUtils.DeleteAndFreeRange<TObjectEx>(A, 2, 4);
  Assert(Length(A) = 3, 'Array length <> 3');
  Assert(TObjectEx.InstanceCount = 3, 'TObjectEx <> 3 instances');
  Constraint := function (const AElem: TObjectEx): Boolean
    begin
      Result := (AElem.ID = 'C') or (AElem.ID = 'D') or (AElem.ID = 'E');
    end;
  Assert(
    not TArrayUtils.Some<TObjectEx>(A, Constraint),
    'C, D, or E found in array'
  );

  // Tidy up remaining objects
  for Obj in A do
    Obj.Free;
  Assert(TObjectEx.InstanceCount = 0, 'TObjectEx <> 0 instances');
end;

Example #2

The second example uses the overload of DeleteAndFreeRange<T: class> that takes only start index of a range as a parameter.

procedure DeleteAndFreeRange_Eg2;
var
  A: TArray<TObjectEx>;
  Obj: TObjectEx;
  Constraint: TArrayUtils.TConstraint<TObjectEx>;
begin
  // Start with no objects
  Assert(TObjectEx.InstanceCount = 0, 'TObjectEx <> 0 instances');

  // Create array of 6 objects
  A := TArray<TObjectEx>.Create(
    TObjectEx.Create('A'), TObjectEx.Create('B'),
    TObjectEx.Create('C'), TObjectEx.Create('D'),
    TObjectEx.Create('E'), TObjectEx.Create('F')
  );
  Assert(Length(A) = 6, 'Array length <> 6');
  Assert(TObjectEx.InstanceCount = 6, 'TObjectEx <> 4 instances');
  Assert(A[2].ID = 'C', 'A[2] <> C');
  Assert(A[3].ID = 'D', 'A[3] <> D');
  Assert(A[4].ID = 'E', 'A[4] <> E');
  Assert(A[5].ID = 'F', 'A[4] <> F');

  // Delete and free all objects from index 2 to the end of the array
  TArrayUtils.DeleteAndFreeRange<TObjectEx>(A, 2);
  Assert(Length(A) = 2, 'Array length <> 2');
  Assert(TObjectEx.InstanceCount = 2, 'TObjectEx <> 2 instances');
  Constraint := function (const AElem: TObjectEx): Boolean
    begin
      Result := (AElem.ID = 'C') or (AElem.ID = 'D')
        or (AElem.ID = 'E') or (AElem.ID = 'F');
    end;
  Assert(
    not TArrayUtils.Some<TObjectEx>(A, Constraint),
    'C, D, E or F found in array'
  );

  // Tidy up remaining objects
  for Obj in A do
    Obj.Free;
  Assert(TObjectEx.InstanceCount = 0, 'TObjectEx <> 0 instances');
end;

See Also