delphi - 为什么在Delphi XE5中{$IFDEF MSWINDOWS}被替换为{$IF Defined(MSWINDOWS)}？

Question

在XE5中所有条件编译如

{$IFDEF MSWINDOWS} 

替换为

{$IF defined(MSWINDOWS)}

例如XE4中的System.Diagnostics.pas有

...
implementation

{$IFDEF MSWINDOWS}
uses Winapi.Windows;
{$ENDIF}
{$IFDEF MACOS}
uses Macapi.Mach;
{$ENDIF}

{ TStopwatch }
...

现在在 XE5 中它看起来像:

...
implementation
{$IF defined(MSWINDOWS)}
uses Winapi.Windows;
{$ELSEIF defined(MACOS)}
uses Macapi.Mach;
{$ELSEIF defined(POSIX)}
uses Posix.Time;
{$ENDIF}

{ TStopwatch }
...

是否有任何特殊原因我也应该迁移类似的调用？

Answer 1

根据 Delphi 文档:

http://docwiki.embarcadero.com/RADStudio/Rio/en/Conditional_compilation_%28Delphi%29

The conditional directives {$IFDEF}, {$IFNDEF}, {$IF}, {$ELSEIF}, {$ELSE}, {$ENDIF}, and {$IFEND} allow you to compile or suppress code based on the status of a conditional symbol.

{$IFDEF} 和 {$IFNDEF} 只允许您使用之前由 {$DEFINE ...} 设置的定义>.
然而 {$IF ..} 指令更加灵活，因为:

Delphi identifiers cannot be referenced in any conditional directives other than {$IF} and {$ELSEIF}.

const LibVersion = 6;  //One constant to define the libversion.
{$IF LibVersion >= 10.0}
  do stuff that covers LibVersion 10,11 and 12
{$ELSEIF Libversion > 5.0}
  do other stuff that covers LibVersion 6,7,8,9
{$IFEND}

如果你尝试使用定义来做到这一点，你就必须这样做

{$DEFINE Lib1}
{$DEFINE Lib2}
{$DEFINE Lib3}
{$DEFINE Lib4}
{$DEFINE Lib5}
{$DEFINE Lib6} //all previous versions have to be defined.

{$IFDEF Lib10}
  do stuff that covers LibVersion 10, 11 and 12
{$ELSE}
  {$IFDEF Lib6}
    do stuff that covers LibVersion 6,7,8,9
  {$ENDIF}
{$ENDIF}

这只是处理定义的稍微高级的版本。
{$IF ..} 表示法更强大，它允许您查询常量表达式而不仅仅是定义。

{$IF ..} 指令是在 Delphi 6 中引入的。

我猜 Embarcadero 决定清理代码库。