CC#17286: Garbage Collector for Delphi Objects and Components: https://cc.embarcadero.com/Item/17286
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| <html> | |
| <head> | |
| <title>Garbage Collector For Delphi Objects and Components</title> | |
| </head> | |
| <body> | |
| <b>Garbage Collector For Delphi Objects and Components</b><br> | |
| <p> </p> | |
| <blockquote class="abstract"><b>Abstract: </b>Automatic memory management | |
| of Delphi objects and components. By Rossen Assenov.</blockquote> | |
| <p> </p> | |
| <p>One of the fundamental questions in object oriented programming is how | |
| the memory management of objects should be done. Different languages | |
| take different approaches. C++ calls the constructor/destructor of | |
| stack allocated objects automaticaly, but for heap allocated objects | |
| you have to do it manually and there is no try..finally statement. In | |
| Java you create the objects when you need them and the garabage collector | |
| takes care of the memory cleanup, but there are no destructors, so you | |
| can not explictly say you don't need an object anymore and there is little | |
| control over the process of garbage collection.<br> | |
| <br> | |
| Delphi provides three ways of object management :<br> | |
| <br> | |
| 1. Create/destroy the objects using try..finally.<br> | |
| 2. Use TComponent descendants - create a component and | |
| let its owner free it.<br> | |
| 3. Interfaces - when the reference count for an interface | |
| becomes 0 the object which implements it is destroyed.<br> | |
| <br> | |
| Interfaces are great for new development - start using | |
| them ! ;) - but sometimes they can be an overhead because there are | |
| two declarations of the same thing. Also, most of the base VCL classes | |
| - TList, TStream, etc. - are not components or interface enabled - | |
| so you have to create/destroy them explicitly.</p> | |
| <h3>THE OBJECT SAFE</h3> | |
| The Delphi help says you shouldn't mix the TComponent | |
| owner approach with the interface memory management, but as always | |
| the forbidden fruit is the sweetest ;). As you'll see it is really | |
| useful to have a TComponent descendant which implements an interface | |
| and at the same time IS reference counted so when it goes out of scope | |
| it frees itself and all the components it owns. We'll extend it so it | |
| keeps a list of TObjects and frees them too.<br> | |
| <br> | |
| Lets name the interface IObjectSafe and the reference counted | |
| TComponent descendent which implements it - TObjectSafe.<br> | |
| <p>Here is the source code for <i>SafeUnit.pas</i> :</p> | |
| <pre class="sourcecode"><code><br><b>unit</b> SafeUnit;<br><br><b>interface</b><br><br><b>uses</b> Classes;<br><br><b>type</b> IObjectSafe = <b>interface</b><br> <b>function</b> Safe : TComponent;<br><br> <b>function</b> New (<b>out</b> aReference <font color="#003399"><i>{: Pointer}</i></font>;<br> <b>const</b> aObject : TObject) : IObjectSafe;<br><br> <b>procedure</b> Guard (<b>const</b> aObject : TObject);<br><br> <b>procedure</b> Dispose (<b>var</b> aReference <font color="#003399"><i>{: Pointer}</i></font>);<br> <b>end</b>;<br><br> IExceptionSafe = <b>interface</b><br> <b>procedure</b> SaveException;<br> <b>end</b>;<br><br><b>function</b> ObjectSafe : IObjectSafe; overload;<br><b>function</b> ObjectSafe (<b>out</b> aObjectSafe : IObjectSafe) : IObjectSafe; overload;<br><b>function</b> ExceptionSafe : IExceptionSafe;<br><br><b>function</b> IsAs (<b>out</b> aReference <font color="#003399"><i>{: Pointer}</i></font>;<br> <b>const</b> aObject : TObject;<br> <b>const</b> aClass : TClass) : Boolean;<br><br><b>implementation</b><br><br><b>uses</b> Windows, SysUtils;<br><br><b>type</b> TExceptionSafe = <b>class</b> (TInterfacedObject, IExceptionSafe)<br> <b>private</b><br> FMessages : <b>String</b>;<br> <b>public</b><br> <b>destructor</b> Destroy; override;<br><br> <b>procedure</b> SaveException;<br> <b>end</b>;<br><br> TInterfacedComponent = <b>class</b> (TComponent)<br> <b>private</b><br> FRefCount : Integer;<br> <b>protected</b><br> <b>function</b> _AddRef : Integer; <b>stdcall</b>;<br> <b>function</b> _Release : Integer; <b>stdcall</b>;<br> <b>public</b><br> <b>procedure</b> BeforeDestruction; override;<br> <b>end</b>;<br><br> TAddObjectMethod = <b>procedure</b> (<b>const</b> aObject : TObject) <b>of</b> <b>object</b>;<br><br> TObjectSafe = <b>class</b> (TInterfacedComponent, IObjectSafe)<br> <b>private</b><br> FObjects : <b>array</b> <b>of</b> TObject;<br> FEmptySlots : <b>array</b> <b>of</b> Integer;<br> AddObject : TAddObjectMethod;<br><br> <b>procedure</b> AddObjectAtEndOfList (<b>const</b> aObject : TObject);<br> <b>procedure</b> AddObjectInEmptySlot (<b>const</b> aObject : TObject);<br><br> <b>procedure</b> RemoveObject (<b>const</b> aObject : TObject);<br> <b>public</b><br> <b>constructor</b> Create (aOwner : TComponent); override;<br> <b>destructor</b> Destroy; override;<br><br> <b>function</b> Safe : TComponent;<br> <b>function</b> New (<b>out</b> aReference;<br> <b>const</b> aObject : TObject) : IObjectSafe;<br> <b>procedure</b> Guard (<b>const</b> aObject : TObject);<br> <b>procedure</b> Dispose (<b>var</b> aReference) ;<br> <b>end</b>;<br><br><b>function</b> TInterfacedComponent._AddRef : Integer;<br><b>begin</b><br> Result := InterlockedIncrement (FRefCount);<br><b>end</b>;<br><br><b>function</b> TInterfacedComponent._Release : Integer;<br><b>begin</b><br> Result := InterlockedDecrement (FRefCount);<br><br> <b>if</b> Result = 0<br> <b>then</b> Destroy;<br><b>end</b>;<br><br><b>procedure</b> TInterfacedComponent.BeforeDestruction;<br><b>begin</b><br> <b>if</b> FRefCount <> 0<br> <b>then</b> <b>raise</b> Exception.Create (ClassName + <font color="#9933cc">' not freed correctly'</font>);<br><b>end</b>;<br><br><font color="#003399"><i>{ TObjectSafe }</i></font><br><br><b>constructor</b> TObjectSafe.Create (aOwner : TComponent);<br><b>begin</b><br> <b>inherited</b> Create (aOwner);<br><br> AddObject := AddObjectAtEndOfList;<br><b>end</b>;<br><br><b>destructor</b> TObjectSafe.Destroy;<br> <b>var</b> aIndex : Integer;<br> aComponent : TComponent;<br><b>begin</b><br> <b>with</b> ExceptionSafe <b>do</b><br> <b>begin</b><br> <b>for</b> aIndex := High (FObjects) <b>downto</b> Low (FObjects) <b>do</b><br> <b>try</b><br> FObjects [aIndex].Free;<br> <b>except</b><br> SaveException;<br> <b>end</b>;<br><br> <b>for</b> aIndex := Pred (ComponentCount) <b>downto</b> 0 <b>do</b><br> <b>try</b><br> aComponent := Components [aIndex];<br> <b>try</b><br> RemoveComponent (aComponent);<br> <b>finally</b><br> aComponent.Free;<br> <b>end</b>;<br> <b>except</b><br> SaveException;<br> <b>end</b>;<br><br> <b>try</b><br> <b>inherited</b> Destroy;<br> <b>except</b><br> SaveException;<br> <b>end</b>;<br> <b>end</b>;<br><b>end</b>;<br><br><b>function</b> TObjectSafe.Safe : TComponent;<br><b>begin</b><br> Result := Self;<br><b>end</b>;<br><br><b>procedure</b> TObjectSafe.AddObjectAtEndOfList (<b>const</b> aObject : TObject);<br><b>begin</b><br> SetLength (FObjects, Succ (Length (FObjects)));<br> FObjects [High (FObjects)] := aObject;<br><b>end</b>;<br><br><b>procedure</b> TObjectSafe.AddObjectInEmptySlot (<b>const</b> aObject : TObject);<br><b>begin</b><br> FObjects [FEmptySlots [High (FEmptySlots)]] := aObject;<br> SetLength (FEmptySlots, High (FEmptySlots));<br><br> <b>if</b> Length (FEmptySlots) = 0<br> <b>then</b> AddObject := AddObjectAtEndOfList;<br><b>end</b>;<br><br><b>procedure</b> TObjectSafe.RemoveObject (<b>const</b> aObject : TObject);<br> <b>var</b> aIndex : Integer;<br><b>begin</b><br> <b>for</b> aIndex := High (FObjects) <b>downto</b> Low (FObjects) <b>do</b><br> <b>begin</b><br> <b>if</b> FObjects [aIndex] = aObject <b>then</b><br> <b>begin</b><br> FObjects [aIndex] := <b>Nil</b>;<br><br> SetLength (FEmptySlots, Succ (Length (FEmptySlots)));<br> FEmptySlots [High (FEmptySlots)] := aIndex;<br> AddObject := AddObjectInEmptySlot;<br> <br> Exit;<br> <b>end</b>;<br> <b>end</b>;<br><b>end</b>;<br><br><b>procedure</b> TObjectSafe.Dispose (<b>var</b> aReference);<br><b>begin</b><br> <b>try</b><br> <b>try</b><br> <b>if</b> TObject (aReference) <b>is</b> TComponent<br> <b>then</b> RemoveComponent (TComponent (TObject (aReference)))<br> <b>else</b> RemoveObject (TObject (aReference));<br> <b>finally</b><br> TObject (aReference).Free;<br> <b>end</b>;<br> <b>finally</b><br> TObject (aReference) := <b>Nil</b>;<br> <b>end</b>;<br><b>end</b>;<br><br><b>procedure</b> TObjectSafe.Guard (<b>const</b> aObject : TObject);<br><b>begin</b><br> <b>try</b><br> <b>if</b> aObject <b>is</b> TComponent <b>then</b><br> <b>begin</b><br> <b>if</b> TComponent (aObject).Owner <> Self<br> <b>then</b> InsertComponent (TComponent (aObject));<br> <b>end</b><br> <b>else</b> AddObject (aObject);<br> <b>except</b><br> aObject.Free;<br><br> <b>raise</b>;<br> <b>end</b>;<br><b>end</b>;<br><br><b>function</b> TObjectSafe.New (<b>out</b> aReference; <b>const</b> aObject : TObject) : IObjectSafe;<br><b>begin</b><br> <b>try</b><br> Guard (aObject);<br><br> TObject (aReference) := aObject;<br> <b>except</b><br> TObject (aReference) := <b>Nil</b>;<br><br> <b>raise</b>;<br> <b>end</b>;<br><br> Result := Self;<br><b>end</b>;<br><br><font color="#003399"><i>{ TExceptionSafe }</i></font><br><br><b>destructor</b> TExceptionSafe.Destroy;<br><b>begin</b><br> <b>try</b><br> <b>if</b> Length (FMessages) > 0<br> <b>then</b> <b>raise</b> Exception.Create (FMessages);<br> <b>finally</b><br> <b>try</b> <b>inherited</b> Destroy; <b>except</b> <b>end</b>;<br> <b>end</b>;<br><b>end</b>;<br><br><b>procedure</b> TExceptionSafe.SaveException;<br><b>begin</b><br> <b>try</b><br> <b>if</b> (ExceptObject <> <b>Nil</b>) <b>and</b> (ExceptObject <b>is</b> Exception)<br> <b>then</b> FMessages := FMessages + Exception (ExceptObject).Message + #13#10;<br> <b>except</b><br> <b>end</b>; <br><b>end</b>;<br><br><b>function</b> ExceptionSafe : IExceptionSafe;<br><b>begin</b><br> Result := TExceptionSafe.Create;<br><b>end</b>;<br><br><b>function</b> ObjectSafe : IObjectSafe;<br><b>begin</b><br> Result := TObjectSafe.Create (<b>Nil</b>);<br><b>end</b>;<br><br><b>function</b> ObjectSafe (<b>out</b> aObjectSafe : IObjectSafe) : IObjectSafe; overload;<br><b>begin</b><br> Result := ObjectSafe;<br><br> aObjectSafe := Result;<br><b>end</b>;<br><br><b>function</b> IsAs (<b>out</b> aReference <font color="#003399"><i>{: Pointer}</i></font>;<br> <b>const</b> aObject : TObject;<br> <b>const</b> aClass : TClass) : Boolean;<br><b>begin</b><br> Result := (aObject <> <b>Nil</b>) <b>and</b> (aObject <b>is</b> aClass);<br><br> <b>if</b> Result<br> <b>then</b> TObject (aReference) := aObject;<br><b>end</b>;<br><br><b>end</b>.<br><br></code></pre> | |
| <p>How do you use a safe ? It's pretty simple :<br> | |
| </p> | |
| <pre class="sourcecode"><code><br><b>procedure</b> TestTheSafe;<br><br> <b>var</b> aMyObject : TMyObject;<br> aMyComponent : TMyComponent;<br><br><b>begin</b><br> <b>with</b> ObjectSafe <b>do</b><br> <b>begin</b><br> New (aMyObject, TMyObject.Create);<br><br> <font color="#003399"><i>// or</i></font><br> <font color="#003399"><i>// aMyObject := TMyObject.Create; Guard (aMyObject);</i></font><br> <br> aMyComponent := TMyComponent.Create (Safe);<br> <b>end</b>;<br><b>end</b>;<br><br></code></pre> | |
| <p>Notice the use of the 'with' statement - you can use a safe without | |
| having to declare a local variable for it. When you create a component just | |
| pass the 'safe' component as the owner to the constructor. When the | |
| execution of the code reaches the 'end' of the 'with' statement the reference | |
| count of IObjectSafe will hit 0, the destructor of TObjectSafe will be called | |
| and all the components and objects it owns will be freed. So now you have | |
| the best of both worlds - you can create an object when you need it, be sure | |
| it will be automaticaly destroyed and know exactly when it will happen.<br> | |
| <br> | |
| The 'New'/'Dispose' methods of IObjectSafe use the 'untyped' | |
| pointer type to return a reference to an object - this will cause | |
| exception if you mismatch the types of the reference and the actual | |
| object created (there won't be a memory leak though), but it is flexible | |
| and shorter to type. If you want to play it safe use the 'Guard' function | |
| instead.<br> | |
| <br> | |
| You can also create one IObjectSafe in the constructor | |
| of a complex object which uses a lot of internal objects so you don't | |
| need to explicitly free them in the destructor.<br> | |
| <br> | |
| Take a look at the implementation of the AddObject 'procedure' | |
| inside TObjectSafe. This is a method pointer technique you can use | |
| when you need to do one operation most of the time - add an object | |
| at the end of the array - and some other operation rarely - put an object | |
| into an empty slot - and you don't want to check each time which one | |
| of them to perform.<br> | |
| </p> | |
| <h3>THE EXCEPTION SAFE</h3> | |
| <p>Another useful safe used in the implementation of TObjectSafe is IExceptionSafe. | |
| Many times you need to perform an action over many objects but sometimes | |
| you can get an exception. The usual practice is to write something | |
| like :</p> | |
| <pre class="sourcecode"><code><br><b>for</b> aIndex := 1 <b>to</b> 10 <b>do</b><br><b>try</b><br> <font color="#003399"><i>// do something which might raise an exception</i></font><br><b>except</b><br><b>end</b>;<br><br></code></pre> | |
| <p>and ignore the exceptions, but it's better to remember the exception | |
| messages and show them later.<br> | |
| <br> | |
| That's what IExceptionSafe is used for. It has only one procedure | |
| 'SaveException' without parameters - it uses the system function 'ExceptObject' | |
| to get a pointer to the current exception. Create a new ExceptionSafe | |
| interface at the start of the block where you want to remember the exceptions | |
| and when the execution reaches the end of the 'with' statement the destructor | |
| of TExcetionSafe checks if there were any exceptions remembered and raises | |
| a new exception with all of the exception messages :<br> | |
| </p> | |
| <pre class="sourcecode"><code><br><b>with</b> ExceptionSafe <b>do</b><br><b>try</b><br> <b>for</b> aIndex := 1 <b>to</b> 10 <b>do</b><br> <b>try</b><br> <font color="#330099"><i>// do something which might raise an exception</i></font><br> <b>except</b><br> SaveException; <br> <b>end</b>;<br><br> <b>for</b> aIndex := 10 <b>to</b> 20 <b>do<br> try</b><br> </code><code><font color="#330099"><i>// do something which might raise an exception</i></font></code><br><code> <b>except</b><br> SaveException; <br> <b>end</b>;<br><br> </code><code><font color="#330099"><i>// do something which might raise an exception</i></font></code><br><code><b>except</b><br> SaveException;<br><b>end</b>;<br><br></code></pre> | |
| <h3>THE 'IsAs' OPERATOR</h3> | |
| <p>Often you need to check the type of some object and typecast it to a | |
| reference using the 'is' and 'as' operators, like this :</p> | |
| <pre class="sourcecode"><code><br><b>if</b> aSomeObject <b>is</b> TMyObject <b>then</b><br><b>begin</b><br> aMyObject := aSomeObject <b>as</b> TMyObject;<br><br> <font color="#330099"><i>// do something with aMyObject</i></font><br><b>end</b>;<br><br></code></pre> | |
| <p>With the 'IsAs' function you can accomplish all this in just one line | |
| : </p> | |
| <pre class="sourcecode"><code><br><b>if</b> IsAs (aMyObject, aSomeObject, TMyObject) <b>then<br>begin</b><br> <font color="#330099"><i>// do something with aMyObject</i></font><br><b>end</b>;<br><br></code></pre> | |
| <p>As you can see 'untyped' pointer types can be quite handy.</p> | |
| <h3>CONCLUSION</h3> | |
| <p>By using the presented techniques you can greatly simplify the memory | |
| management of Delphi objects/components and make your programs safer.<br> | |
| Suggestions and comments are welcomed -- just <a href="mailto:rossen_assenov@yahoo.com"> | |
| write me</a>!<br> | |
| The source code is available at <a href="http://codecentral.borland.com/codecentral/ccweb.exe/listing?id=17286"> | |
| CodeCentral</a><br> | |
| </p> | |
| </body> | |
| </html> |
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| // Viewing SafeUit.pas from CC#17286: Garbage Collector for Delphi Objects and Components | |
| unit SafeUnit; | |
| interface | |
| uses Classes; | |
| type IObjectSafe = interface | |
| function Safe : TComponent; | |
| function New (out aReference {: Pointer}; | |
| const aObject : TObject) : IObjectSafe; | |
| procedure Guard (const aObject : TObject); | |
| procedure Dispose (var aReference {: Pointer}); | |
| end; | |
| IExceptionSafe = interface | |
| procedure SaveException; | |
| end; | |
| function ObjectSafe : IObjectSafe; overload; | |
| function ObjectSafe (out aObjectSafe : IObjectSafe) : IObjectSafe; overload; | |
| function ExceptionSafe : IExceptionSafe; | |
| function IsAs (out aReference {: Pointer}; | |
| const aObject : TObject; | |
| const aClass : TClass) : Boolean; | |
| implementation | |
| uses Windows, SysUtils; | |
| type TExceptionSafe = class (TInterfacedObject, IExceptionSafe) | |
| private | |
| FMessages : String; | |
| public | |
| destructor Destroy; override; | |
| procedure SaveException; | |
| end; | |
| TInterfacedComponent = class (TComponent) | |
| private | |
| FRefCount : Integer; | |
| protected | |
| function _AddRef : Integer; stdcall; | |
| function _Release : Integer; stdcall; | |
| public | |
| procedure BeforeDestruction; override; | |
| end; | |
| TAddObjectMethod = procedure (const aObject : TObject) of object; | |
| TObjectSafe = class (TInterfacedComponent, IObjectSafe) | |
| private | |
| FObjects : array of TObject; | |
| FEmptySlots : array of Integer; | |
| AddObject : TAddObjectMethod; | |
| procedure AddObjectAtEndOfList (const aObject : TObject); | |
| procedure AddObjectInEmptySlot (const aObject : TObject); | |
| procedure RemoveObject (const aObject : TObject); | |
| public | |
| constructor Create (aOwner : TComponent); override; | |
| destructor Destroy; override; | |
| function Safe : TComponent; | |
| function New (out aReference; | |
| const aObject : TObject) : IObjectSafe; | |
| procedure Guard (const aObject : TObject); | |
| procedure Dispose (var aReference) ; | |
| end; | |
| function TInterfacedComponent._AddRef : Integer; | |
| begin | |
| Result := InterlockedIncrement (FRefCount); | |
| end; | |
| function TInterfacedComponent._Release : Integer; | |
| begin | |
| Result := InterlockedDecrement (FRefCount); | |
| if Result = 0 | |
| then Destroy; | |
| end; | |
| procedure TInterfacedComponent.BeforeDestruction; | |
| begin | |
| if FRefCount <> 0 | |
| then raise Exception.Create (ClassName + ' not freed correctly'); | |
| end; | |
| { TObjectSafe } | |
| constructor TObjectSafe.Create (aOwner : TComponent); | |
| begin | |
| inherited Create (aOwner); | |
| AddObject := AddObjectAtEndOfList; | |
| end; | |
| destructor TObjectSafe.Destroy; | |
| var aIndex : Integer; | |
| aComponent : TComponent; | |
| begin | |
| with ExceptionSafe do | |
| begin | |
| for aIndex := High (FObjects) downto Low (FObjects) do | |
| try | |
| FObjects [aIndex].Free; | |
| except | |
| SaveException; | |
| end; | |
| for aIndex := Pred (ComponentCount) downto 0 do | |
| try | |
| aComponent := Components [aIndex]; | |
| try | |
| RemoveComponent (aComponent); | |
| finally | |
| aComponent.Free; | |
| end; | |
| except | |
| SaveException; | |
| end; | |
| try | |
| inherited Destroy; | |
| except | |
| SaveException; | |
| end; | |
| end; | |
| end; | |
| function TObjectSafe.Safe : TComponent; | |
| begin | |
| Result := Self; | |
| end; | |
| procedure TObjectSafe.AddObjectAtEndOfList (const aObject : TObject); | |
| begin | |
| SetLength (FObjects, Succ (Length (FObjects))); | |
| FObjects [High (FObjects)] := aObject; | |
| end; | |
| procedure TObjectSafe.AddObjectInEmptySlot (const aObject : TObject); | |
| begin | |
| FObjects [FEmptySlots [High (FEmptySlots)]] := aObject; | |
| SetLength (FEmptySlots, High (FEmptySlots)); | |
| if Length (FEmptySlots) = 0 | |
| then AddObject := AddObjectAtEndOfList; | |
| end; | |
| procedure TObjectSafe.RemoveObject (const aObject : TObject); | |
| var aIndex : Integer; | |
| begin | |
| for aIndex := High (FObjects) downto Low (FObjects) do | |
| begin | |
| if FObjects [aIndex] = aObject then | |
| begin | |
| FObjects [aIndex] := Nil; | |
| SetLength (FEmptySlots, Succ (Length (FEmptySlots))); | |
| FEmptySlots [High (FEmptySlots)] := aIndex; | |
| AddObject := AddObjectInEmptySlot; | |
| Exit; | |
| end; | |
| end; | |
| end; | |
| procedure TObjectSafe.Dispose (var aReference); | |
| begin | |
| try | |
| try | |
| if TObject (aReference) is TComponent | |
| then RemoveComponent (TComponent (TObject (aReference))) | |
| else RemoveObject (TObject (aReference)); | |
| finally | |
| TObject (aReference).Free; | |
| end; | |
| finally | |
| TObject (aReference) := Nil; | |
| end; | |
| end; | |
| procedure TObjectSafe.Guard (const aObject : TObject); | |
| begin | |
| try | |
| if aObject is TComponent then | |
| begin | |
| if TComponent (aObject).Owner <> Self | |
| then InsertComponent (TComponent (aObject)); | |
| end | |
| else AddObject (aObject); | |
| except | |
| aObject.Free; | |
| raise; | |
| end; | |
| end; | |
| function TObjectSafe.New (out aReference; const aObject : TObject) : IObjectSafe; | |
| begin | |
| try | |
| Guard (aObject); | |
| TObject (aReference) := aObject; | |
| except | |
| TObject (aReference) := Nil; | |
| raise; | |
| end; | |
| Result := Self; | |
| end; | |
| { TExceptionSafe } | |
| destructor TExceptionSafe.Destroy; | |
| begin | |
| try | |
| if Length (FMessages) > 0 | |
| then raise Exception.Create (FMessages); | |
| finally | |
| try inherited Destroy; except end; | |
| end; | |
| end; | |
| procedure TExceptionSafe.SaveException; | |
| begin | |
| try | |
| if (ExceptObject <> Nil) and (ExceptObject is Exception) | |
| then FMessages := FMessages + Exception (ExceptObject).Message + #13#10; | |
| except | |
| end; | |
| end; | |
| function ExceptionSafe : IExceptionSafe; | |
| begin | |
| Result := TExceptionSafe.Create; | |
| end; | |
| function ObjectSafe : IObjectSafe; | |
| begin | |
| Result := TObjectSafe.Create (Nil); | |
| end; | |
| function ObjectSafe (out aObjectSafe : IObjectSafe) : IObjectSafe; overload; | |
| begin | |
| Result := ObjectSafe; | |
| aObjectSafe := Result; | |
| end; | |
| function IsAs (out aReference {: Pointer}; | |
| const aObject : TObject; | |
| const aClass : TClass) : Boolean; | |
| begin | |
| Result := (aObject <> Nil) and (aObject is aClass); | |
| if Result | |
| then TObject (aReference) := aObject; | |
| end; | |
| end. |
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