Resources for the D programming language

D is a systems programming language that makes formal correctness practical for high-performance software. Created by Walter Bright in 2001, D brings Design by Contract (the rigorous specification methodology pioneered by Eiffel) directly into a native-compiled, C-interoperable systems language, eliminating the traditional trade-off between performance and program verification.

D implements contracts through in, out, and invariant blocks as first-class language features, not library add-ons. This native support combines with compile-time function execution (CTFE), allowing developers to verify logic and generate code at compile time, and built-in unit testing that makes correctness checks integral to the development workflow. The language offers the low-level control and performance of C++ while adding modern features like optional garbage collection, powerful template metaprogramming, and seamless C interoperability.

D is used in game development, scientific computing, high-frequency trading, and systems programming where both execution speed and program correctness are non-negotiable. Its design philosophy is simple: formal methods shouldn't require sacrificing performance, and systems programmers shouldn't have to choose between speed and reliability. For developers who want Eiffel's correctness guarantees with C++'s performance profile, D delivers both.

The C++ alternative with native Design by Contract support

D shipped native Design by Contract in 2001: preconditions, postconditions, and class invariants as first-class syntax. in (amount <= balance) isn't a comment or a separate unit test; it's the requirement itself, enforced at function boundaries and catching violations before they cascade. This collapses redundant work: teams write specifications as comments, tests, and monitoring alerts. DbC makes the specification executable once. Every null reference exception is an undeclared precondition. Every "this should never happen" comment is an unenforced invariant.

D proved native DbC works in a C-syntax systems language. Rust won mainstream adoption anyway by enforcing safety at compile time. Bugs can't compile, period. D's contracts catch logic bugs at runtime, and only if teams keep them enabled. The market chose mandatory compile-time correctness over optional runtime checks. DbC survived only where external forces demand it: Ada with SPARK in regulated avionics, Dafny in formal verification, Racket in PL research. D occupied the middle ground nobody wanted: stronger than asserts, weaker than proofs, and bypassable when inconvenient.

Beyond contracts, D delivers on its systems programming fundamentals: compile times competitive with C, runtime performance matching C++, metaprogramming that actually works without template error novels, and interoperability with C that doesn't require FFI ceremony.