D — Systems Programming Language Bridging High-Level and Low-Level Code

Introduction

D is a systems programming language designed as a practical alternative to C and C++. It retains compatibility with C ABIs and header files while adding modern features such as garbage collection, first-class functions, and compile-time evaluation. D has been in development since 2001 and is maintained by the D Language Foundation.

What D Does

• Compiles to efficient native code via DMD, LDC (LLVM), or GDC (GCC) backends
• Provides direct C and C++ ABI interoperability without wrappers
• Supports compile-time function execution (CTFE) for code generation
• Includes a standard library (Phobos) with ranges, algorithms, and concurrency
• Offers optional garbage collection with the ability to use manual memory management

Architecture Overview

D has three compiler implementations: DMD (reference compiler), LDC (LLVM-based for optimized output), and GDC (GCC-based). All produce native binaries. The language supports a unique range-based iteration model that underpins the standard library algorithms. CTFE allows arbitrary D code to execute at compile time, enabling powerful metaprogramming without separate tooling.

Self-Hosting & Configuration

• Install DMD or LDC via package managers, or use the install.sh script from dlang.org
• Manage projects and dependencies with dub, the D package manager and build tool
• Configure builds in dub.json or dub.sdl files
• Cross-compile using LDC with target triple flags
• Use rdmd for script-like execution of single-file programs

Key Features

• Three compiler backends (DMD, LDC, GDC) for different optimization needs
• Compile-time function execution (CTFE) for zero-cost abstractions
• String mixins and template metaprogramming for code generation
• Ranges and algorithms for composable lazy data processing
• Direct extern(C) and extern(C++) interop with existing codebases

Comparison with Similar Tools

• C++ — C++ has a larger ecosystem but more complexity; D simplifies many patterns while maintaining similar performance
• Rust — Rust enforces memory safety via borrow checking; D offers optional GC and a gentler learning curve
• Go — Go is simpler with built-in concurrency; D provides more low-level control and metaprogramming
• Nim — Nim compiles via C with Python-like syntax; D has C/C++ syntax familiarity and three mature compiler backends
• Zig — Zig is minimal with no hidden control flow; D is higher-level with GC, exceptions, and a rich standard library

FAQ

Q: Is D garbage collected? A: D includes an optional GC. You can disable it and use manual memory management or allocators for performance-critical code.

Q: Can D call C libraries directly? A: Yes. D supports extern(C) declarations, and tools like dstep can auto-generate D bindings from C headers.

Q: Who uses D in production? A: Companies including eBay, Netflix, and Mercedes-Benz have used D for performance-sensitive backend systems and tooling.

Q: How does CTFE work? A: Any D function without side effects can be evaluated at compile time. The compiler literally runs the function during compilation and embeds the result in the binary.

Sources

• https://github.com/dlang/dmd
• https://dlang.org/documentation.html