这是返回空通用值的正确方法吗？

Question

我有一个HashTable,我需要一些方法来返回not_found结果.

type
  TCell<T> = record
  .....
    property key: cardinal read FKey write FKey;
    property data: T read FData write FData;
  end;

  THashTable<T> = class(TEnumerable<T>)
  private
    FCells: array of TCell<T>;
    FEmpty: T;
  ...
    constructor Create(InitialSize: cardinal); overload;
    function Lookup(key: cardinal): T;
  ...
  end;

constructor THashTable<T>.Create(InitialSize: cardinal);
begin
  inherited Create;
  // Initialize regular cells
  FArraySize:= InitialSize;
  Assert((FArraySize and (FArraySize - 1)) = 0); // Must be a power of 2
  SetLength(FCells, FArraySize);

  FillChar(FEmpty, SizeOf(FEmpty), #0);  //Superfluous I know, just there to
                                         //demonstrate the point. 
end;

鉴于上述结构,我该如何返回not found结果？
如果我有指针,我会返回nil指针T.
但是不允许指向泛型类型的指针.

所以我想出了下面的解决方案:

function THashTable<T>.Lookup(key: cardinal): T;
var
  Cell: NativeUInt;
begin
  if (key <> 0) then begin
    // Check regular cells
    Cell:= First_Cell(IntegerHash(key));
    while (true) do begin
      if (FCells[Cell].key = key) then Exit(FCells[Cell].data);
      if not (FCells[Cell].key = 0) then Exit(FEmpty);  <<-- is this correct?
      Cell:= Circular_Next(Cell);
    end;
  end else begin
    Result:= FEmpty;   <<--- Can I return an empty generic like this?
  end;
end;

我可以将零初始化通用返回到什么意思no result？

或者我会遇到结构化类型(类/记录/变体/字符串等)的问题.

请注意,我确实理解T整数时的歧义.零可能是一个有效的值,因此它与not_found无法区分.
我并不担心这些结果.

Answer 1

您正在寻找的是default(T),对于任何类型T,它将返回零值.