Claude-Tools-for-Delphi: Skill for Claude Code

Delphi memory & exceptions — reference

Class instances are freed manually, on every target — desktop and mobile alike, no GC. Every ownerless Create must be freed on every path, the exception path included. The checklist at the end is the single source of truth: the light-review-step1 and light-review-step3 agents read this file and apply it, so keep the list here and nowhere else.

try immediately after Create

Anything between Create and try can raise and leak the instance.

LList := TStringList.Create;
try
  LList.Add('item');
finally
  LList.Free;
end;

Several locals: nest try..finally in reverse creation order, or nil them all up front and FreeAndNil each in one finally.

Functions that return an object — guard the newborn

If a later step raises before the caller receives the result, it leaks:

function BuildList: TStringList;
begin
  Result := TStringList.Create;
  try
    Fill(Result);        // may raise
  except
    Result.Free;         // free before propagating
    raise;
  end;
end;

Never pass an inline .Create as a parameter unless the callee definitely takes ownership.

FreeAndNil vs Free · Owner-managed

• FreeAndNil(F) for a field that may be re-tested with Assigned or freed twice; plain Free for a local that dies at end of scope.
• A component created with an Owner — TButton.Create(Self) — is freed by that Owner. Do not free it yourself.
• Owned fields allocated in a constructor are freed in the destructor, inherited last.

Exceptions: specific, never swallowed

Catch the narrowest type you can act on. A bare except ... end hides EAccessViolation, EOutOfMemory and real bugs.

try
  Commit;
except
  on E: EFDDBEngineException do
  begin
    Log(E.Message);
    raise EDatabaseError.Create('Service temporarily unavailable');  // translate to a domain error
  end;
end;

• Re-raise with a bare raise; — raise E; resets the stack trace.
• Prefer a small domain tree (EBusinessRule / EInfrastructure and their subclasses) over scattered raise Exception.Create('...'), so upper layers can catch by category.