TBoldGuard¶

TBoldGuard provides automatic memory management for local objects using Delphi's interface reference counting. When the guard goes out of scope, all tracked objects are freed automatically — even if an exception occurs.

Class Hierarchy¶

classDiagram
    TBoldRefCountedObject <|-- TBoldGuard
    TBoldGuard ..|> IBoldGuard

    TBoldGuard : +Create(var v0..v9)
    TBoldGuard : -fObjectVariable[0..9]
    TBoldGuard : +Destroy() frees all

Class Definition¶

IBoldGuard = interface(IUnknown)
end;

TBoldGuard = class(TBoldRefCountedObject, IBoldGuard)
public
  // Overloaded constructors for 1 to 10 variables
  constructor Create(var v0); overload;
  constructor Create(var v0, v1); overload;
  constructor Create(var v0, v1, v2); overload;
  // ... up to 10 variables
  constructor Create(var v0, v1, v2, v3, v4, v5, v6, v7, v8, v9); overload;
  destructor Destroy; override;
end;

How It Works¶

Declare a local IBoldGuard variable (interface type)
Assign TBoldGuard.Create(var1, var2, ...) — constructor sets all variables to nil
Create objects and assign to the tracked variables
When the procedure exits (normally or by exception), the interface ref count drops to 0
Destroy frees all non-nil tracked objects in reverse order

This pattern predates Delphi's ARC and is similar to Go's defer or Python's context managers.

Before and After¶

Without TBoldGuard¶

procedure ProcessData;
var
  List: TStringList;
  Stream: TFileStream;
  Parser: TParser;
begin
  List := nil;
  Stream := nil;
  Parser := nil;
  try
    List := TStringList.Create;
    Stream := TFileStream.Create('data.txt', fmOpenRead);
    Parser := TParser.Create;

    // ... use objects ...

  finally
    Parser.Free;
    Stream.Free;
    List.Free;
  end;
end;

With TBoldGuard¶

procedure ProcessData;
var
  Guard: IBoldGuard;
  List: TStringList;
  Stream: TFileStream;
  Parser: TParser;
begin
  Guard := TBoldGuard.Create(List, Stream, Parser);
  // All three are now nil and will be freed automatically

  List := TStringList.Create;
  Stream := TFileStream.Create('data.txt', fmOpenRead);
  Parser := TParser.Create;

  // ... use objects ...
  // No try/finally needed — Guard frees everything on exit
end;

Common Patterns¶

Bold Source Code Usage¶

TBoldGuard is used extensively throughout Bold's source code:

procedure TBoldOcl.Evaluate(const Expr: string);
var
  Guard: IBoldGuard;
  Env: TBoldOclEnvironment;
  Node: TBoldOLWNode;
begin
  Guard := TBoldGuard.Create(Env, Node);
  Env := TBoldOclEnvironment.Create;
  Node := ParseExpression(Expr);
  // ... evaluate ...
end;  // Env and Node freed automatically

Maximum 10 Variables¶

The guard supports up to 10 variables (MAXARRAY = 9, zero-indexed). If you need more, use multiple guards or reconsider your design.

var
  Guard1, Guard2: IBoldGuard;
  A, B, C, D, E, F, G, H, I, J: TObject;
  K, L: TObject;
begin
  Guard1 := TBoldGuard.Create(A, B, C, D, E, F, G, H, I, J);
  Guard2 := TBoldGuard.Create(K, L);
  // ...
end;

Variables are set to nil

The constructor sets all passed variables to nil. You don't need to initialize them yourself. Only non-nil objects are freed in the destructor.