如何为互相依赖的记录定义隐式转换运算符？ [英] How do I define implicit conversion operators for mutually dependent records?

问题描述

我在Delphi 2006中使用操作符重载记录（请不要回答这个问题，告诉我不要。）

I am using the operator overloading for records in Delphi 2006. (Please don't answer this question by telling me not to.)

我有两种记录类型其中隐式运算符重载。它们只是在实现模块的同时，不通过接口暴露出来。

I have two record types with the implicit operator overloaded. They are both only in the implementation of the module, not exposed through the interface.

我的问题是，现在他们是相互依赖的，我不知道如何将第二个类型声明为编译器。我知道如何使用函数，过程和类，但不能使用记录。

My problem is, now that they are mutually dependent, I don't know how to forward declare the second type to the compiler. I know how to do this with functions, procedures, and classes, but not with records.

这是一个简单的例子，我正在尝试：

Here is a simplified example of what I am trying to do:

implementation

type
  TMyRec1 = record
    Field1 : Integer;
    class operator Implicit(a: TMyRec2): TMyRec1;  // <---- Undeclared Identifier here.
  end;

  TMyRec2 = record
    Field2: Integer;
    class operator Implicit(a: TMyRec1): TMyRec2;
  end;

class operator TMyRec1.Implicit(a:TMyRec2): TMyRec1;
begin
  Result.Field1 := a.Field2;
end;

class operator TMyRec2.Implicit(a:TMyRec2): TMyRec2;
begin
  Result.Field2 := a.Field1;
end;

推荐答案

您不能对记录类型有转发声明。定义第二种类型的隐式运算符：

You can't have forward declarations for record types. Define both Implicit operators in the second type:

type
  TMyRec1 = record
    Field1 : Integer;
  end;

  TMyRec2 = record
    Field2: Integer;
    class operator Implicit(a: TMyRec2): TMyRec1;
    class operator Implicit(a: TMyRec1): TMyRec2;
  end;

从帮助：

隐式只有在绝对必要的时候才应提供转换，应避免反身。最好让类型B隐式地将其自身转换为类型A，而类型A不知道类型B（反之亦然）。

Implicit conversions should be provided only where absolutely necessary, and reflexivity should be avoided. It is best to let type B implicitly convert itself to type A, and let type A have no knowledge of type B (or vice versa).

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