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name: patterns/observer description: Observer Pattern (Callbacks) pattern for C development

Observer Pattern (Callbacks)

Objects register interest in events and get notified when they occur. In C, implemented as callback function pointers with context.

ikigai Application

Streaming chunks: LLM client notifies REPL as response chunks arrive:

Copytypedef void (*chunk_callback_t)(void *ctx, const char *chunk, size_t len);
res_t ik_llm_stream(client, messages, on_chunk, user_ctx);

Terminal resize: Signal handler notifies REPL of SIGWINCH.

Future uses:

• Database change notifications
• Tool execution progress
• Background task completion

Convention: Always pair callback function pointer with void *user_ctx parameter.