C++ OTL: Object Token Library

Expressive, Safe, Consistent.

The C++ Object Token Library (CppOtl) provides a set of tokens that are designed to manage an object's lifetime, similar to smart pointers from the C++ standard library. CppOtl contains tokens for unique and shared ownership of objects, weak observers for them, adds a unified type of ownership. Also, it introduces tokens with single (not_null) multiplicity, which can mitigate the "null references: billion-dollar mistake".

Tokens from CppOtl are integrated with smart pointers from the C++ standard library and can be consistently converted from one to another. CppOtl is intended for cases when there is not enough functionality of smart pointers from the C++ standard library and additional capabilities are required.

Features

1. A set of consistent tokens that can express associative links, function parameters and variables according to a UML model.
2. single tokens that always have a linked object and can not be empty.
3. trackable and untrackable tokens for appropriate use-case requirements.
4. The safe::weak can be created both from the safe::unique and the safe::shared. It will become expired (but not dangling) when an owner of a watched object is destroyed.
5. The safe::unified can temporarily prolong an object's lifetime in a given scope that allows finishing work with an object even other tokens is destroyed.
6. A constructor with the itself parameter allows a token itself to create an object with given attributes.
7. Algorithms for unified access to object tokens.
8. Tokens meet the requirements of std::ranges::range, that allows to pass them to functions that accept range argument.
9. Traits allow recognizing characteristics of tokens in compile-time.
10. Focusing on maximum error detection in compile-time, several assertions in a debug build, minimum overhead in a release build, avoiding exceptions.
11. The ability to integrate CppOtl tokens with third-party pointers and tokens.

Tokens

All CppOtl entities are located in the otn namespace. otn is an abbreviation for object token.

• safe tokens provide an object's lifetime safety and can not be dangling.

  Name	Description
  safe::unique[_single]<T>	A unique single owner of an object.
  safe::unique_optional<T>	A unique optional owner of an object.
  safe::shared[_single]<T>	A shared single owner of an object.
  safe::shared_optional<T>	A shared optional owner of an object.
  safe::weak_optional<T>	An optional observer of an object owned by the safe::unique or safe::shared.
  safe::unified[_single]<T>	A unified single carrier and accessor of an object linked with safe tokens.
  safe::unified_optional<T>	A unified optional carrier and accessor of an object linked with safe tokens.

• slim tokens are lightweight with minimum runtime overhead.

  Name	Description
  slim::unique[_single]<T, D>	A unique single owner of an object.
  slim::unique_optional<T, D>	A unique optional owner of an object.

• raw tokens are close to raw C++ objects and pointers.

  Name	Description
  raw::unique[_single]<T>	A unique single owner of an object.
  raw::unique_optional<T>	A unique optional owner of an object.
  raw::weak[_single]<T>	A single observer of an object.
  raw::weak_optional<T>	An optional observer of an object.
  raw::unified[_single]<T>	A unified single carrier and accessor of an object.
  raw::unified_optional<T>	A unified optional carrier and accessor of an object.

Using otn tokens is similar to using smart pointers from the C++ standard library.

Reference

• Characteristics
• Synopsis
• Construction
• Access
• Traits
• UML relations

Requirements

C++17 compiler.

Tested with:

• GCC 9.2.1
• Clang 9.0.1

Note: It is a known issue that not all compilers can compile SFINAE "magic" from the otn/support/concept.hpp. Use C++20 standard in this case, if a compiler supports C++20 Concepts.

Usage

CppOtl is a header-only library.

Copy the include/otn directory to a compiler accessible place, add the path obtained to include to a compiler's include paths, and include the otn/all.hpp header file in a source code file.

Examples

See the Example complex.

Tests

See the Test/Token complex.

Current state

Beta version. Improving functionality, eliminating bugs, optimizing unoptimals.