ruby
Instance variables versus class variables in Ruby: what @ and @@ actually mean, why an @ variable set at the class level stays empty when read from an instance, and how @@ values are shared by every instance. Short code samples make each behavior easy to verify.
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Pattern matching in Ruby turns case statements into a precise switch over data shapes: match and destructure hashes from an API response, combine several patterns in one branch, capture values across patterns, and validate configuration. Ruby 2.7+ syntax examples.
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Running shell commands from Ruby: system, backticks, exec, the IO class, spawn, and Open3.popen3 compared with pros and cons, from quick one-liners to capturing stdout, stderr, and exit status, so you can pick the right method for scripts and production code.
Database sharding in Rails step by step: create a separate database per shard, wire them up in database.yml, and query across them. Plus how sharding differs from partitioning, with a native PostgreSQL partitioning example done through Rails migrations.
Sidekiq basic_fetch vs super_fetch: open source Sidekiq fetches jobs with BRPOP and loses them when a process crashes, while Sidekiq Pro's super_fetch uses RPOPLPUSH with private per-process queues to recover orphaned jobs. What that means for queue reliability.
Generic types in TypeScript let one function, class, or interface work safely with many data types. What generics are, how a type parameter beats hardcoding a concrete entity type in a validation helper, and honest pros and cons before you use them everywhere.
Domain Driven Design in Ruby with a working example: aggregates, entities, value objects, and repositories built around a ProductCatalog, then extended with event-driven design and event sourcing, where projections rebuild state from events instead of a database.