JCL中由接口获得对象的方法

我原本并不想单独发以下JCL的方法，可是想到很多人可能还是不知道的。另外，从我博客的回复上看，很多人也愿意去了解一下，特此贴出JCL中的代码。

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       // 
       ===Interfaceinformation================================================== 
       
 
       
functionGetImplementorOfInterface( 
       const 
       I:IInterface):TObject;
 
       ... 
       {TODO-cDOC:OriginalcodebyHallvardVassbotn} 
       
 
       ... 
       {TODO-cTesting:Checktheimplemetationforanyfurtherversionofcompiler} 
       
 
       const 
       
AddByte 
       = 
       $ 
       04244483 
       ; 
       // 
       opcodeforADDDWORDPTR[ESP+4],Shortint 
       
 
       AddLong 
       = 
       $ 
       04244481 
       ; 
       // 
       opcodeforADDDWORDPTR[ESP+4],Longint 
       
 
       type
PAdjustSelfThunk 
       = 
        
       ^ 
       TAdjustSelfThunk;
TAdjustSelfThunk 
       = 
       packedrecord
 
       case 
       AddInstruction:Longintof
AddByte:(AdjustmentByte:ShortInt);
AddLong:(AdjustmentLong:Longint);
end;
PInterfaceMT 
       = 
        
       ^ 
       TInterfaceMT;
TInterfaceMT 
       = 
       packedrecord
QueryInterfaceThunk:PAdjustSelfThunk;
end;
TInterfaceRef 
       = 
        
       ^ 
       PInterfaceMT;
var
QueryInterfaceThunk:PAdjustSelfThunk;
begin
 
       try 
       
Result: 
       = 
       Pointer(I);
 
       if 
       Assigned(Result)then
begin
QueryInterfaceThunk: 
       = 
       TInterfaceRef(I) 
       ^ 
       .QueryInterfaceThunk;
 
       case 
       QueryInterfaceThunk.AddInstructionof
AddByte:
Inc(PChar(Result),QueryInterfaceThunk.AdjustmentByte);
AddLong:
Inc(PChar(Result),QueryInterfaceThunk.AdjustmentLong);
 
       else 
       
Result: 
       = 
       nil;
end;
end;
except
Result: 
       = 
       nil;
end;
end;
 
      
 
     

注释：这段代码出自JCL代码中JclSysUtils单元中。

提示：读这段代码，要明白一个道理，在代码执行过程中，接口和对象指针的偏移是硬编码的在汇编中的。转换的过程，就是解析这段汇编的过程。