Difference between revisions of "Overriding Destructors"
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| − | The only task of a destructor is freeing resources allocated | + | The only task of a destructor is freeing resources allocated by the constructor and other methods (some resources may be allocated on-demand only). In any case the destructor must leave the object in the same state as right after ''DoSuperMethod()/DoSuperNew()'' in the constructor. After that the destructor calls a super class destructor. The destructor receives an empty message. |
IPTR MyClassDispose(Class *cl, Object *obj, Msg msg) | IPTR MyClassDispose(Class *cl, Object *obj, Msg msg) | ||
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| − | The example destructor follows | + | The example destructor follows the example of the constructor in the [[Overriding Constructors]] article. Three resources obtained in the constructor are freed here. The destructor is also prepared for a partially constructed object, every resource is checked against ''NULL'' before freeing. If for some type of resource NULL is a valid handle, an additional flag may be added to the object instance data area. |
Revision as of 06:50, 7 January 2011
Grzegorz Kraszewski
The only task of a destructor is freeing resources allocated by the constructor and other methods (some resources may be allocated on-demand only). In any case the destructor must leave the object in the same state as right after DoSuperMethod()/DoSuperNew() in the constructor. After that the destructor calls a super class destructor. The destructor receives an empty message.
IPTR MyClassDispose(Class *cl, Object *obj, Msg msg)
{
struct MyClassData *d = (struct MyClassData*)INST_DATA(cl, obj);
if (d->ResourceA) FreeResourceA();
if (d->ResourceB) FreeResourceB();
if (d->ResourceC) FreeResourceC();
return DoSuperMethodA(cl, obj, msg);
}
The example destructor follows the example of the constructor in the Overriding Constructors article. Three resources obtained in the constructor are freed here. The destructor is also prepared for a partially constructed object, every resource is checked against NULL before freeing. If for some type of resource NULL is a valid handle, an additional flag may be added to the object instance data area.