Inline Small Functions for Best Perf

Rule

Mark small functions as inline so the compiler can eliminate call overhead and optimize across the call boundary.

• •Prefer inline for: one-liners, trivial getters/setters, small predicates, hot-path helpers.
• •In headers: use inline on function definitions that are defined in the header (so multiple TUs can include them without ODR issues).
• •In .cpp: use inline on small functions that are only used in that TU, to encourage inlining.

When to Use

1. •Header-defined functions: Any function whose definition lives in a header should be inline (or in an anonymous namespace in the header) to avoid multiple-definition errors and to allow inlining.
2. •Small accessors: Getters/setters that return a member or do a simple assignment are good candidates.
3. •Hot path: Small functions called in loops or critical paths benefit from inlining.
4. •Tiny helpers: Functions that are a few statements and called from few call sites.

Examples

// Header: inline so definition can appear in header and still inline at call sites
inline int Foo::getValue() const { return value_; }
inline void Foo::setValue(int v) { value_ = v; }

// Small predicate
inline bool isReady() const { return state_ == Ready; }

Caveats

• •Do not force inline on large or rarely-called functions; it can increase code size and hurt I-cache.
• •The compiler may ignore inline for optimization; use it as a hint. For forced inlining, use compiler-specific attributes (e.g. __attribute__((always_inline))) only when profiling shows a need.
• •In C++, member functions defined inside the class body are implicitly inline; no need to repeat inline there.