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Project: Array Utilities Unit
Unit: DelphiDabbler.Lib.ArrayUtils
Record: TArrayUtils
Applies to: ~>0.1
class function Slice<T>(const A: array of T;
AStartIndex, AEndIndex: Integer): TArray<T>;
overload; static;
class function Slice<T>(const A: array of T;
AStartIndex: Integer): TArray<T>;
overload; static;
Returns an array comprising a contiguous range of elements from an array.
The elements of the returned array are shallow copies of the corresponding elements of the original array, so any references within the resulting array are the same as those in the initial array.
The original array is not modified.
Parameters:
A - The array from which the slice is to be taken. If A is empty then all slices are also empty.
AStartIndex - The index of the first element of A that is to be included in the slice.
If AStartIndex ≤ 0 then the slice begins at the first element of A.
If AStartIndex ≥ Length(A) then an empty array is returned.
AEndIndex - Optional parameter that specified the index of the last element of A that is to be included in the slice.
If AEndIndex is omitted or AEndIndex ≥ Length(A) then the slice continues to the end of A.
If AEndIndex < AStartIndex then an empty array is returned.
Returns:
If the returned array needs to have deep copies of the the original array elements then pass the return value of Slice<T> to the deep copying overload of Copy<T>, along with a suitable TCloner<T> implementation.
This example shows the most flexible use of Slice<T> where both the start and end indexes are provided:
procedure Slice_Eg1;
var
A, ASlice, AExpectedSlice: TArray<string>;
begin
A := TArray<string>.Create('a', 'stitch', 'in', 'time', 'saves', 'nine');
// slice from the start of A
ASlice := TArrayUtils.Slice<string>(A, 0, 2);
AExpectedSlice := TArray<string>.Create('a', 'stitch', 'in');
Assert(TArrayUtils.Equal<string>(AExpectedSlice, ASlice, SameStr));
// slice in the middle of A
ASlice := TArrayUtils.Slice<string>(A, 2, 4);
AExpectedSlice := TArray<string>.Create('in', 'time', 'saves');
Assert(TArrayUtils.Equal<string>(AExpectedSlice, ASlice, SameStr));
// slice at the end of A
ASlice := TArrayUtils.Slice<string>(A, 4, 5);
AExpectedSlice := TArray<string>.Create('saves', 'nine');
Assert(TArrayUtils.Equal<string>(AExpectedSlice, ASlice, SameStr));
end;
This second example show the use of the basic version of Slice<T> where only the start index is provided:
procedure Slice_Eg2;
var
A, ASlice, AExpectedSlice: TArray<string>;
begin
A := TArray<string>.Create('a', 'stitch', 'in', 'time', 'saves', 'nine');
// slice from mid to end of A
ASlice := TArrayUtils.Slice<string>(A, 3);
AExpectedSlice := TArray<string>.Create('time', 'saves', 'nine');
Assert(TArrayUtils.Equal<string>(AExpectedSlice, ASlice, SameStr));
// slice of all of A
ASlice := TArrayUtils.Slice<string>(A, 0);
AExpectedSlice := A;
Assert(TArrayUtils.Equal<string>(AExpectedSlice, ASlice, SameStr));
end;