exceptions.txt

<div dir="ltr" style="text-align: left;" trbidi="on">
Íè äëÿ êîãî íàâåðíîå íå îòêðîþ Àìåðèêó, íî âñ¸ æå íàïèøó.<br />
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Ìîæíî ñäåëàòü òàê:<br />
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<pre class="brush:delphi">type
 EmyException = class(Exception)
 end;//EmyException
...
if not Condition1 then
 raise EMyException.Create('Some string1');
...
if not Condition2 then
 raise EMyException.Create('Some string2');
</pre>
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À ìîæíî òàê:
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<pre class="brush:delphi">type
 EmyException = class(Exception)
  public
   class procedure Check(aCondition: Boolean; 
                         const aMessage: String);
 end;//EmyException
...
class procedure EmyException.Check(aCondition: Boolean; 
                                   const aMessage: String);
begin
 if not aCondition then
  raise Self.Create(aMessage);
end;
...
EMyException.Check(Condition1, 'Some string1');
...
EMyException.Check(Condition2, 'Some string2');
</pre>
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Âðîäå "òî æå íà òî æå", è îáà âàðèàíòà - îäèíàêîâûå.
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Íî ïî ìíå - âòîðîé âàðèàíò - "âêóñíåå". Äà è ÷èòàáåëüíåå.<br />
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È â îòëàäêå - ïîëåçíåå.<br />
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Ïî÷åìó â îòëàäêå ïîëåçíåå? Ïîòîìó, ÷òî ìîæíî ïîñòàâèòü <b>îäèí</b> break-point â EmyException.Check, à íå ìíîæåñòâî ïî êîäó.<br />
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Âîçìîæíî â íîâûõ âåðñèÿõ Delphi ýòî âõîäèò â ñòàíäàðòíóþ áèáëèîòåêó. Íå çíàþ, ÷åñòíî - íå ïðîâåðÿë. Íî ìû ýòèì ïîäõîäîì ïîëüçóåìñÿ óæå <b>î÷åíü äàâíî</b>. È îí íàì íðàâèòñÿ.<br />
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È åãî ïîíÿòíîå äåëî - ìîæíî ðàñøèðÿòü è óñîâåðøåíñòâîâàòü.<br />
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Íàïðèìåð - íå ïåðåäàâàòü ñòðîêó, à "ãåíåðèðîâàòü" å¸ âíóòðè Check. Íó â îáùåì - âàðèàíòîâ ìàññà.<br />
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Íó è åù¸ îòìå÷ó - ÿ íàáëþäàë äîñòàòî÷íîå êîëè÷åñòâî ëþäåé, êîòîðûå çàáûâàëè raise.<br />
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Ò.å. ïèñàëè òàê:<br />
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<pre class="brush:delphi"> Exception.Create('aMessage');
</pre>
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à íå òàê:
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<pre class="brush:delphi"> raise Exception.Create('aMessage');
</pre>
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Íó è ïðî "ðàñøèðåíèÿ".<br />
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Ìîæíî íàïðèìåð òàê:
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<pre class="brush:delphi">type
 TMyPredicate = reference to function (aData: Integer): Boolean;
 EmyException = class(Exception)
  public
   class procedure Check(aCondition: Boolean; 
                         const aMessage: String); overload;
   class procedure Check(aCondition: TMyPredicate; 
                         const aMessage: String; 
                         aData: Integer); overload;
 end;//EmyException
...
class procedure EmyException.Check(aCondition: Boolean; 
                                   const aMessage: String);
begin
 if not aCondition then
  raise Self.Create(aMessage);
end;

class procedure EmyException.Check(aCondition: TMyPredicate; 
                                   const aMessage: String; 
                                   aData: Integer);
begin
 if not aCondition(aData) then
  raise Self.Create('InvalidData: ' + IntToStr(aData) + aMessage);
end;

...
EMyException.Check(Condition1, 'Some string1');
...
EMyException.Check(
 function (aData: Integer): Boolean; 
 begin 
  Result := IsValid(aData); 
 end;, 
 'Some string2', 
 SomeComplexExpression);
</pre>
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-- íó ïîíÿòíîå, äåëî, ÷òî ýòî "ìàêåò", à íå ðåàëüíî ðàáî÷èé êîä.
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×åì ýòîò "ìàêåò" õîðîø? Òåì, ÷òî&nbsp;SomeComplexExpression - âû÷èñëèòñÿ <b>îäèí</b> ðàç.<br />
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Ïîíÿòíîå äåëî, ÷òî ìîæíî è "ëîêàëüíîé ïåðåìåííîé" îáîéòèñü.<br />
Íó ýòî â ïðîñòåéøèõ ñëó÷àÿõ.&nbsp;
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Äà è ïîòîì, âåäü ìîæíî íàïèñàòü è òàê:
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<pre class="brush:delphi">var
 SomeLocalData : Integer;

EMyException.Check(
 function (aData: Integer): Boolean; 
 begin 
  Result := (aData = SomeLocalData); 
 end;, 
 'Some string2', 
 SomeComplexExpression);
</pre>
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Update.&nbsp;
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Ïî ìîòèâàì êîììåíòàðèÿ - <a href="http://programmingmindstream.blogspot.ru/2014/08/blog-post_85.html?showComment=1408566592655#c1216957169742679866">http://programmingmindstream.blogspot.ru/2014/08/blog-post_85.html?showComment=1408566592655#c1216957169742679866</a><br />
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Ïðî "ïðîñòî ïðîöåäóðó" - ìû êîíå÷íî æå òîæå èìè ïîëüçîâàëèñü:

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<pre class="brush:delphi">function Ht(ID : LongInt) : LongInt;
{var
 nDosError : SmallInt; // Ñþäà çàíåñóò êîä, âîçâðàùåííûé ÄÎÑ
 nOperation: SmallInt; // Ñþäà çàíåñóò êîä îïåðàöèè, ïðèâåäøåé ê îøèáêå
 lErrstr : array[0..1000] of AnsiChar;
 lErrstr2 : PAnsiChar;
}
begin
 Result := ID;

 if lNeedStackOut_ErrNum &lt;&gt; 0 then
 begin
  l3System.Stack2Log(Format('HTERROR = %d STACK OUT', [lNeedStackOut_ErrNum]));
  lNeedStackOut_ErrNum := 0;
 end;

{ if ID = -1 then
  lErrstr2 := htExtError(nDosError, nOperation, @lErrstr[0]);
}
 if ID &lt; 0 then
  raise EHtErrors.CreateInt(ID);
end;
....
   Ht(htOpenResults(Masks,ROPEN_READ,@FldArr,FldCount));
....
     Ht(htDeleteRecords(TmpList));
....
     Ht(htOpenResults(ValList,ROPEN_READ,nil,0));
</pre>
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È åù¸.<br />
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×òî ñëó÷èòñÿ, åñëè ìû íàïèøåì òàê:
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<pre class="brush:delphi">type
 EmyException2 = class(EmyException)
 end;//EmyException2

...
EmyException2.Check(aCondition, aMessage);
</pre>
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-- èñêëþ÷åíèå êàêîãî êëàññà âîçáóäèòñÿ?<br />
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EmyException èëè EmyException2?<br />
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EmyException2 :-) ÷òî è "ñëåäîâàëî îæèäàòü".<br />
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Ýòî ê âîïðîñó - "ïî÷åìó ìåòîä êëàññà, à íå ïðîñòî ôóíêöèÿ".<br />
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Update.<br />
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(Â íåêîòîðîì ðîäå â îòâåò íà - http://programmingmindstream.blogspot.ru/2014/08/blog-post_85.html?showComment=1408649403323#c8271514992700352647)<br />
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Âîò êñòàòè ïðèìåð, òîãî ÷òî íàïèñàíî â ñàìîì íà÷àëå:
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<pre class="brush:delphi">Em3InvalidStreamPos.Check(Self.IsValidPosition,
                          aHeader.f_Name,
                          l_Pos);
Em3InvalidStreamSize.Check(Self.IsValidPosition,
                           aHeader.f_Name,
                           aHeader.f_TOCItemData.rBody.rRealSize);
Em3InvalidStreamPos.Check(Self.IsValidLink,
                          aHeader.f_Name,
                          aHeader.f_TOCItemData.rBody.RTOCBuffRootPosition);
Em3InvalidStreamPos.Check(Self.IsValidLink,
                          aHeader.f_Name,
                          aHeader.f_TOCItemData.rBody.RTOCItemListPosition);
Em3InvalidStreamPos.Check(Self.IsValidLink,
                          aHeader.f_Name,
                          aHeader.f_TOCItemData.RNextPosition);
</pre>
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- IsValidPosition è IsValidLink ýòî ïðåäèêàòû.<br />
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Ò.å. function (aData: Int64): Boolean of object;<br />
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Check â äàííîì ñëó÷àå âûãëÿäèò òàê:
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<pre class="brush:delphi">type
 TInt64Predicate = function (aData: Int64): Boolean of object;
...
class procedure Em3InvalidStreamData.Check(aCondition: TInt64Predicate;
                                           aName : String;
                                           aData : Int64);
begin
 if not aCondition(aData) then
  raise Self.CreateFmt('Invalid data %d in file %s', [aName, aData]);
end; 
...
Em3InvalidStreamPos = class(Em3InvalidStreamData);

Em3InvalidStreamSize = class(Em3InvalidStreamData);
</pre>
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-- çà÷åì åù¸ ýòî íóæíî?<br />
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Íó ÷òîáû ñ ôîðìàòêàìè â ôóíêöèè Format íå íàïóòàòü.
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È íå îòëàæèâàòü "íàâåä¸ííûé" exception êîòîðûé âûëåçåò ó ïîëüçîâàòåëÿ, íî "íå ðàññêàæåò ïðàâäó".<br />
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Ïîíÿòíîå äåëî, ÷òî ïðèìåð êîäà - äàëåêî íå ñàìûé "êðàñèâûé", íî ÿ ñïåöèàëüíî íè÷åãî íå ðàôèíèðîâàë.<br />
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Êîíå÷íî - íà âêóñ è öâåò - "âñå ôëîìàñòåðû ðàçíûå", íî ìíå ëè÷íî ýòî íðàâèòñÿ áîëüøå, ÷åì ñ "âÿçàíêîé" raise.<br />
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Ïîïðîáóéòå íàïèñàòü ñ raise è ïîêàæèòå - ÷òî îí "áóäåò êîðî÷å". ß áóäó ðàä ïîó÷èòüñÿ.<br />
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È êñòàòè äà - âûâîä ñòåêà â ëîã - ïîìîãàåò èäåíòèôèöèðîâàòü ñòðîêó - îòêóäà ïîëåòåëî èñêëþ÷åíèå. Íî ïðî ýòî ÿ ìîæåò áûòü åù¸ êîãäà-íèáóäü íàïèøó îòäåëüíî. <br />
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(Ïîêà âîò <a href="http://programmingmindstream.blogspot.ru/2014/08/blog-post_22.html">òóò</a> - èä¸ò íåêîòîðàÿ äèñêóññèÿ)<br />
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Update.<br />
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Äà è îãîâîðþñü.<br />
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Ìîæíî áûëî áû êîíå÷íî "ñî÷èíèòü" ÷òî-òî âðîäå:

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<pre class="brush:delphi">Em3InvalidStreamPos.Check(Self.IsValidPosition,
                          aHeader.f_Name,
                          [l_Pos,
                           aHeader.f_TOCItemData.rBody.rRealSize,
                           aHeader.f_TOCItemData.rBody.RTOCBuffRootPosition,
                           aHeader.f_TOCItemData.rBody.RTOCItemListPosition,
                           aHeader.f_TOCItemData.RNextPosition]);
</pre>
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-- íî ÿ <b>îñîçíàííî</b> ýòîãî íå äåëàþ.<br />
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Ò.ê. êîíå÷íî çàïèñü êîðî÷å è "÷èòàáåëüíåå".
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Íî!  òàêîì âàðèàíòå - ñëîæíåå èñêàòü <b>ðåàëüíûé</b> èñòî÷íèê îøèáêè.<br />
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Íó è <b>with</b> êîíå÷íî òîæå ìîæíî áûëî áû íàïèñàòü. ß çíàþ. Íî <b>ÿ ëè÷íî</b> - "èäåîëîãè÷åñêèé ïðîòèâíèê" with.<br />
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Îñîáåííî â âàðèàíòå Delphi, ãäå íåò "îáðàòíîé óñòîé÷èâîñòè".<br />
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Ñëîâà "îáðàòíàÿ óñòîé÷èâîñòü" ïîíÿòíû? Èëè ÿ îïÿòü "âûäóìûâàþ ñâîè òåðìèíû"?<br />
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Íà âñÿêèé ñëó÷àé íàïèñàë âîò ÷òî -&nbsp;<a href="http://programmingmindstream.blogspot.ru/2014/08/blog-post_17.html">Êîðîòêî. Îá "îáðàòíîé óñòîé÷èâîñòè"</a></div>