Finally
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The reserved word finally identifies a block of code that should always be processed, regardless of whether the preceding try block was fully executed or has been exited early (in case of an Exception, Exit, Break or Continue).
Examples
Simple example:
begin
...
try
... // code to check
finally
... // code which should always be executed even if try exits early
end;
...
end;
Example with error handling:
begin
...
try
try
... // code to check
except
... // error handling
end;
finally
... // code which should always be executed even if try exits early
end;
...
end;
Non-Exception Code
Despite the name, Try-Finally is not strictly tied to the usage of exceptions, and also provides benefits in code where no exceptions can be raised. The reason for this is that the Finally block will always be executed, even if the try block exits early.
This can be very useful e.g. for the Break Fast Break Even paradigm, where Exit or other jumps (such as Break or Continue) are used:
function CheckFormat(const CSVString: String): Boolean;
var
sl: TStringList;
begin
Result := False;
sl := TStringList.Create;
try
sl.Delimiter := ';';
sl.StrictDelimiter := True;
sl.DelimitedText := CSVString;
if sl.Count <> RowCount then
Exit; // Will automatically execute the finally block before exiting
// Check field data, e.g.
if not isNumber(sl[1]) then
Exit; // Will automatically execute the finally block before exiting
// ...
finally
sl.Free;
end;
// All checks passed
Result := True;
end;
Because of the try-finally, the code can simply call exit, and the finally block ensures that sl will be freed afterwards. Without the try-finally, each of these blocks would require a seperate sl.Free call:
function CheckFormat(const CSVString: String): Boolean;
var
sl: TStringList;
begin
Result := False;
sl := TStringList.Create;
sl.Delimiter := ';';
sl.StrictDelimiter := True;
sl.DelimitedText := CSVString;
if sl.Count <> RowCount then
begin
sl.Free;
Exit;
end;
if not isNumber(sl[1]) then
begin
sl.Free;
Exit;
end;
// ...
sl.Free;
end;
Therefore try-finally can even in code without exceptions, help to ensure that the cleanup is performed, without having to consider each exit point individually
Caveats
The finally part is not executed if a halt occurred.
