Crystal Interview Questions and Answers for experienced

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100 Crystal Interview Questions and Answers

  1. What is Crystal and what are its key features?

    • Answer: Crystal is a statically-typed, compiled language that aims to combine the performance of C with the developer experience of Ruby. Key features include: its speed due to compilation to native code, its type system that catches errors at compile time, its concise and expressive syntax inspired by Ruby, its garbage collection with minimal pauses, its metaprogramming capabilities, and its strong concurrency support using fibers.

  2. Explain Crystal's type system. How does it differ from dynamically-typed languages like Ruby?

    • Answer: Crystal has a static type system, meaning types are checked at compile time. This contrasts with Ruby's dynamic typing, where type checking happens at runtime. Crystal's type inference reduces boilerplate, but you can explicitly declare types. The static nature helps catch errors early and allows for compiler optimizations, leading to better performance. Crystal also supports duck typing to a degree, allowing you to use objects with the expected methods without strict type matching.

  3. How does Crystal handle concurrency? Explain the use of fibers.

    • Answer: Crystal uses fibers for concurrency, which are lightweight threads managed by the runtime. Fibers are scheduled cooperatively, meaning they yield control explicitly. This avoids the complexities and overhead of preemptive multitasking found in OS threads. Fibers are ideal for I/O-bound operations, as they can switch context when waiting for network or disk operations, keeping CPU usage high.

  4. What is the role of the Crystal compiler? Describe the compilation process.

    • Answer: The Crystal compiler translates Crystal source code into native machine code, resulting in high performance. The process involves several stages: parsing the source code, type checking, optimization, and finally code generation. The compiler uses LLVM as a backend, benefiting from LLVM's extensive optimizations.

  5. Explain Crystal's garbage collection mechanism.

    • Answer: Crystal employs a garbage collector to automatically manage memory. It's a generational garbage collector designed for low pause times. This means that while it reclaims memory automatically, the pauses during garbage collection are minimized, preventing significant performance drops in applications.

  6. How does Crystal's macros system work? Give an example.

    • Answer: Crystal's macros allow you to generate code at compile time. They operate on the abstract syntax tree (AST) of your code. This enables powerful metaprogramming capabilities, such as creating domain-specific languages (DSLs) within Crystal itself. For example, you could create a macro that generates boilerplate code for database interactions.

  7. Describe your experience working with Crystal's standard library.

    • Answer: [This requires a personalized answer based on the candidate's experience. They should describe specific parts of the standard library they've used and how they've found them useful, including things like networking, data structures, or file I/O.]

  8. How would you handle error handling in Crystal? Discuss different approaches.

    • Answer: Crystal uses exceptions for error handling, similar to languages like Ruby or Python. However, Crystal also emphasizes using the `Result` type for handling potential failures more explicitly and safely, allowing you to return either a success value or an error value. This prevents exceptions from unexpectedly interrupting the flow and enables more robust error handling.

  9. Explain the difference between `struct` and `class` in Crystal.

    • Answer: Structs in Crystal are value types, meaning copies are made when they're assigned or passed to functions. Classes are reference types; only a reference is copied. Structs are generally more efficient for simple data structures, while classes are better suited for objects with complex behavior and identity.

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