C++

Reflection & static if in C++26+ Upcoming standards (C++26/29) are moving toward compile-time reflection and easier metaprogramming. However, this is still not a full interpreter it’s a set of built-in reflection primitives.

Cling: A C++ Interpreter Based on Clang/LLVM Cling is a C++ interpreter built on Clang/LLVM. While it’s primarily meant as a REPL, Cling has been explored as a meta-programming backend: Lets you execute C++ code at runtime or compile time interactively. Some research prototypes used Cling as a JIT inside the compiler to do meta-programming, generating code on-the-fly. It’s not fully integrated into clang++ for ahead-of-time compilation, but there’s interest in this space, especially at CERN. ...

Embedded Interpreter for Polyglot C++/Rust programming Imagine a C++ compiler that runs a C++ interpreter at compile time so it can do dynamic code generation (or FFI glue) to call Rust code directly, without hand-writing bindings. That’s exactly the kind of thing a Circle-style compiler or Cling-style integration would make possible. The Idea The compiler has an embedded interpreter that can run arbitrary C++ at compile time. At compile time, it: ...

There are several techniques you can use to achieve function wrapping at compile time with Clang and other compilers. ...

In Progress write more examples in c++ After writing a post about monkey patching in C++ using pointer hacking I thought I’d write about a method that might be cleaner. You can substitute functions at link time to “monkey patch” a C or C++ program, most commonly using the –wrap option of the GNU linker (ld). This technique is typically used for unit testing and debugging, where you can wrap a function and inspect its calls and return values without changing the program’s source code. ...

Monkey Patching changing code at runtime (replacing or adding methods, altering prototypes/classes/modules) without editing the original source. Powerful and dynamic — but risky. Use it deliberately and carefully. Languages that commonly allow/encourage monkey patching Ruby — class reopening and Module#prepend / alias_method make it a classic. Python — functions, methods, modules are mutable objects; you can replace names at runtime. Testing helpers like unittest.mock/pytest facilitate it. JavaScript — modify prototypes, replace functions on objects, or change global objects (e.g., Array.prototype). Node and browsers both permit it. ...

Other Meta programming in Main Stream C++ constexpr & consteval Modern C++ (C++11 through C++26) already has compile-time evaluation via: constexpr functions (C++11+) consteval functions (C++20+) constinit, concepts, reflection proposals, etc. This lets you run limited C++ code at compile time in a standardized way, but it’s not a full interpreter.

The std::fmt library in C++ provides a modern, fast, and type-safe approach to text formatting, drawing inspiration from Python’s str.format syntax. It serves as a more robust and performant alternative to the C-style printf and the C++ iostreams (std::cout). C++ version introduction The core components of the C++ standard library’s formatting capabilities were introduced in C++20. Methods for formatting custom objects For a user-defined type to be formatted by the std::fmt library, you must provide a specialization of the std::formatter template. The required methods within this specialization are: ...

The std::stacktrace library was introduced in C++23, providing a standard, cross-platform way to generate and inspect the call stack at runtime. Before C++23, developers had to rely on platform-specific APIs or third-party libraries, which led to non-portable and inconsistent code. What is std::stacktrace? A stack trace is a record of the function calls that led to a particular point in a program’s execution. The <stacktrace> library defines: std::basic_stacktrace: A class template that stores a sequence of std::stacktrace_entry objects. The common alias std::stacktrace uses the standard allocator. std::stacktrace_entry: A class that represents a single frame in the call stack. If debug information is available, it can provide details such as the function name, source file, and line number. std::stacktrace::current(): A static member function that captures the current call stack. How to use std::stacktrace ...