arrays – 包含动态数组的记录的通用列表

{$APPTYPE CONSOLE}

var
  x,y: array of Integer;

begin
  SetLength(x,1);
  x[0] := 42;
  y := x;
  Writeln(x[0]);
  y[0] := 666;
  Writeln(x[0]);
end.

输出是：

42
666

原因是动态数组是引用类型.分配给动态数组类型的变量时,您将获取另一个引用而不进行复制.

您可以通过强制引用是唯一的(这只是一个简单的引用)来解决这个问题.有很多方法可以实现这一目标.例如,您可以在要唯一的数组上调用SetLength.

{$APPTYPE CONSOLE}

var
  x,1);
  x[0] := 42;
  y := x;
  SetLength(y,Length(y));
  Writeln(x[0]);
  y[0] := 666;
  Writeln(x[0]);
end.

输出：

42
42

所以,在你的代码中,你可以像这样写：

MyList:=TList<TMyRec>.Create;

SetLength(MyRec.MyArr,5);
MyRec.MyArr[0]:=8;  // just for demonstration
MyRec.Name:='Record 1';
MyRec.Completed:=true;
MyList.Add(MyRec);

SetLength(MyRec.MyArr,5); // <-- make the array unique
MyRec.MyArr[0]:=5;  // just for demonstration
MyRec.Name:='Record 2';
MyRec.Completed:=false;
MyList.Add(MyRec);

您可以使用各种其他方法来强制执行唯一性,包括Finalize,分配nil,Copy等.

这个问题在documentation中有详细介绍.以下是相关的摘录：

If X and Y are variables of the same dynamic-array type,X := Y points
X to the same array as Y. (There is no need to allocate memory for X
before performing this operation.) Unlike strings and static arrays,
copy-on-write is not employed for dynamic arrays,so they are not
automatically copied before they are written to. For example,after
this code executes:

06005

the value of A[0] is 2. (If A and B were static arrays,A[0] would
still be 1.) Assigning to a dynamic-array index (for example,
MyFlexibleArray[2] := 7) does not reallocate the array. Out-of-range
indexes are not reported at compile time. In contrast,to make an
independent copy of a dynamic array,you must use the global Copy
function:

06006