record - FreePascal 中不同记录的标识符可以重复吗？

Question

这是我的问题:我想创建一个记录类型，其中在变体记录的情况下，一些(但不是全部)将具有特定字段。根据wiki ，这是完全合法的。然而，当我尝试编译以下代码时:

program example;

{$mode objfpc}{$H+}

uses sysutils;

type
  maritalStates = (single, married, widowed, divorced);

  TPerson = record
    name: record
      first, middle, last: string;
    end;
    sex: (male, female);
    dob: TDateTime;
    case maritalStatus: maritalStates of
      single: ( );
      married, widowed: (marriageDate: TDateTime);
      divorced: (marriageDate, divorceDate: TDateTime;
        isFirstDivorce: boolean)      
  end;

var
  ExPerson: TPerson;

begin
ExPerson.name.first := 'John';
ExPerson.name.middle := 'Bob';
ExPerson.name.last := 'Smith';
ExPerson.sex := male;
ExPerson.dob := StrToDate('05/05/1990');
ExPerson.maritalStatus := married;
ExPerson.marriageDate := StrToDate('04/01/2015');

end.

编译失败并出现以下错误:

$ fpc ex.pas
Free Pascal Compiler version 3.0.0 [2016/02/14] for x86_64
Copyright (c) 1993-2015 by Florian Klaempfl and others
Target OS: Win64 for x64
Compiling ex.pas
ex.pas(19,18) Error: Duplicate identifier "marriageDate"
ex.pas(21,3) Error: Duplicate identifier "marriageDate"
ex.pas(35,4) Fatal: There were 2 errors compiling module, stopping
Fatal: Compilation aborted
Error: C:\lazarus\fpc\3.0.0\bin\x86_64-win64\ppcx64.exe returned an error exitcode

维基是完全错误的，还是我在这里遗漏了一些东西？有什么办法可以达到我想要的效果吗？

Answer 1

非常有趣的问题。我确信这是可能的。如果您将代码修改为:

..
married, widowed, divorced: (marriageDate: TDateTime);
divorced: (divorceDate: TDateTime; isFirstDivorce: boolean)
..

它可以工作，但这不是您想要的结果。由于结婚日期和离婚日期相互重叠(如评论中所述!)

这张图片取自《Pascal 用户手册(第 4 版)》，您可以看到变体部分具有相同的内存位置。

根据Pascal users manual (4th edition)对于“Turbo Pascal ISBN 3-89011-060-6”一书，您引用的 wiki 上描述的记录声明无效!

1. All field names must be distinct - even if they occur in different variants.
2. If a variant is empty (i.e., has no fields), the form is: C:()
3. A field list can have only one variant part and it must follow the fixed part of the record.
4. A variant may itself contain a variant part; hence variant parts can be nested.
5. The scope of enumerated type constant identifiers that are introduced in a record type extends over the enclosing block.

第 1 点与此处相关! 《Turbo Pascal》一书建议的解决方案是对多次出现的字段名称使用唯一的前缀。

在您的情况下，您可能会如下所示:

TPerson = record
    name: record
      first, middle, last: string;
    end;
    sex: (male, female);
    dob: TDateTime;
    case maritalStatus: maritalStates of
      single: ( );
      married, widowed: (marMarriageDate: TDateTime);
      divorced: (divMarriageDate, divorceDate: TDateTime;
        isFirstDivorce: boolean)      
  end;

另一个解决方案是将已婚、离婚......定义为记录类型。

..
married       : (m: TMarried);
divorced      : (d: TDivorced);
..