March 25, 2026 Published on RubyStackNews Ruby is a high-level language. C is a low-level language. At some point, every serious Ruby application needs to cross that boundary. Maybe you need a cryptography library. Maybe a signal processing engine. Maybe a hardware interface. Maybe raw performance on a hot path. There are two ways to…

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Ruby can interoperate with C through two main approaches: the FFI gem and C extensions. The FFI gem lets you bind and call existing C library functions from pure Ruby using a DSL, works across MRI, JRuby, and TruffleRuby, and is naturally compatible with Ruby 3 Ractors for true parallelism. C extensions go deeper — you write C code that integrates with the Ruby runtime via the Ruby C API, allowing C structs to become native Ruby objects with GC integration and zero call overhead, but only on MRI. The post covers installation, type mappings, struct handling, callbacks, Ractor usage with FFI, and the TypedData_Wrap_Struct pattern for C extensions, concluding with a practical decision guide for choosing between the two approaches.

FFI: How Ruby Talks to C