Question

Hi What is the best way to do nested try & finally statements in delphi?

var cds1  : TClientDataSet;     cds2  : TClientDataSet;     cds3  : TClientDataSet;     cds4  : TClientDataSet; begin   cds1      := TClientDataSet.Create(application );   try     cds2      := TClientDataSet.Create(application );     try       cds3      := TClientDataSet.Create(application );       try         cds4      := TClientDataSet.Create(application );         try         ///////////////////////////////////////////////////////////////////////         ///      DO WHAT NEEDS TO BE DONE         ///////////////////////////////////////////////////////////////////////         finally           cds4.free;         end;        finally         cds3.free;       end;     finally       cds2.free;     end;   finally     cds1.free;   end; end; 

Can you Suggest a better way of doing this?

Answer 1

how about the following:

var cds1  : TClientDataSet;     cds2  : TClientDataSet;     cds3  : TClientDataSet;     cds4  : TClientDataSet; begin   cds1      := Nil;   cds2      := Nil;   cds3      := Nil;   cds4      := Nil;   try     cds1      := TClientDataSet.Create(nil);     cds2      := TClientDataSet.Create(nil);     cds3      := TClientDataSet.Create(nil);     cds4      := TClientDataSet.Create(nil);     ///////////////////////////////////////////////////////////////////////     ///      DO WHAT NEEDS TO BE DONE     ///////////////////////////////////////////////////////////////////////   finally     freeandnil(cds4);     freeandnil(cds3);     freeandnil(cds2);     freeandnil(Cds1);   end; end; 

This keeps it compact, and only attempts to free the instances which were created. There really is no need to perform the nesting since ANY failure will result in dropping to the finally and performing all of the cleanup in the example you provided.

Personally I try not to nest within the same method… with the exception being a try/try/except/finally scenario. If I find myself needing to nest, then to me that is a great time to think refactoring into another method call.

EDIT Cleaned up a bit thanks to the comments by mghie and utku.

EDIT changed the object creation to not reference application, as its not necessary in this example.