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Item 27: Minimize casting

Concept​

Casts subvert the type system. Prefer C++-style casts (static_cast, dynamic_cast, const_cast, reinterpret_cast) over C-style casts. Avoid dynamic_cast in performance-sensitive code. Often, a redesign can eliminate the need for casting entirely.

Code Example​

// Prefer static_cast for well-defined conversions
double d = static_cast<double>(numerator) / denominator;

// dynamic_cast is expensive — use virtual functions instead
if (auto* dp = dynamic_cast<Derived*>(basePtr)) {
    dp->special();
}

Full source code

Things to Remember​

  • Avoid casts whenever practical, especially dynamic_cast in performance-sensitive code.
  • When casting is necessary, hide it inside a function.
  • Prefer C++-style casts to old-style casts.
  • Item 3 — Use const whenever possible
  • Item 34 — Differentiate inheritance of interface and implementation