Rust for C-Programmers

16.8 Summary

Rust enforces explicitness and safety in type conversions, diverging significantly from C/C++’s implicit conversion rules and potentially unsafe casting behaviors.

• The as keyword provides direct primitive casting, similar in syntax but not always behavior to C casts (e.g., saturation). It performs no runtime checks and requires programmer vigilance regarding potential data loss or reinterpretation.
• The From/Into traits define idiomatic, infallible (safe) conversions, with Into being automatically provided if From is implemented.
• The TryFrom/TryInto traits handle fallible conversions, returning a Result to ensure error handling, with TryInto being automatically provided if TryFrom is implemented.
• Standard string conversions rely on the Display, ToString (auto-implemented for Display), and FromStr traits, used via formatting macros and the .parse() method respectively.
• std::mem::transmute offers unsafe, low-level bit reinterpretation for specific scenarios but should be used sparingly and with extreme care due to its ability to cause undefined behavior.

By understanding and applying these distinct mechanisms appropriately, C programmers can leverage Rust’s type system to write more robust, maintainable, and safer systems code, avoiding many common conversion-related bugs.