[英]variant record in delphi
I am just trying to learn variant records.Can someone explain how Can I check shape in record whether it is rectangle/Triangle etc. or any good example with implementation available ?我只是想学习变体记录。有人可以解释我如何检查记录中的形状是矩形/三角形等还是任何可用的实现的好例子? I had checked variants record here but no implementation available..我在这里检查了变体记录,但没有可用的实现..
type
TShapeList = (Rectangle, Triangle, Circle, Ellipse, Other);
TFigure = record
case TShapeList of
Rectangle: (Height, Width: Real);
Triangle: (Side1, Side2, Angle: Real);
Circle: (Radius: Real);
Ellipse, Other: ();
end;
You have to add a field for the shape like so:您必须为该形状添加一个字段,如下所示:
type
TShapeList = (Rectangle, Triangle, Circle, Ellipse, Other);
TFigure = record
case Shape: TShapeList of
Rectangle: (Height, Width: Real);
Triangle: (Side1, Side2, Angle: Real);
Circle: (Radius: Real);
Ellipse, Other: ();
end;
Note the Shape
field.注意Shape
字段。
Also note that this doesn't imply any automatic checking by Delphi - you have to do that yourself.另请注意,这并不意味着 Delphi 进行任何自动检查 - 您必须自己进行。 For example, you could make all the fields private and allow access only through properties.例如,您可以将所有字段设为私有并仅允许通过属性进行访问。 In their getter/setter methods you could assign and check the Shape
field as needed.在他们的 getter/setter 方法中,您可以根据需要分配和检查Shape
字段。 Here's a sketch:这是一个草图:
type
TShapeList = (Rectangle, Triangle, Circle, Ellipse, Other);
TFigureImpl = record
case Shape: TShapeList of
Rectangle: (Height, Width: Real);
Triangle: (Side1, Side2, Angle: Real);
Circle: (Radius: Real);
Ellipse, Other: ();
end;
TFigure = record
strict private
FImpl: TFigureImpl;
function GetHeight: Real;
procedure SetHeight(const Value: Real);
public
property Shape: TShapeList read FImpl.Shape;
property Height: Real read GetHeight write SetHeight;
// ... more properties
end;
{ TFigure }
function TFigure.GetHeight: Real;
begin
Assert(FImpl.Shape = Rectangle); // Checking shape
Result := FImpl.Height;
end;
procedure TFigure.SetHeight(const Value: Real);
begin
FImpl.Shape := Rectangle; // Setting shape
FImpl.Height := Value;
end;
I split the record in two types because otherwise the compiler wouldn't accept the visibility specifiers as they are needed.我将记录分成两种类型,否则编译器将不会在需要时接受可见性说明符。 Also I think it's more readable and the GExperts code formatter doesn't choke on it.此外,我认为它更具可读性,并且 GExperts 代码格式化程序不会因此而窒息。 :-) :-)
Now something like this would violate an assertion:现在这样的事情会违反断言:
procedure Test;
var
f: TFigure;
begin
f.Height := 10;
Writeln(f.Radius);
end;
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