Verifying and avoiding copy-on-write overhead
WHAT IT TESTS: CoW mechanics and mutation patterns. OUTLINE: confirm extra copies via isKnownUniquelyReferenced or instruments and the retain trace; ensure unique references, mutate inout/in place, reserveCapacity, avoid aliasing.
WHAT IT TESTS: understanding why a CoW copy fires and how to prevent it. ANSWER OUTLINE: verify by profiling for unexpected memcpy or retain spikes, or by checking uniqueness in custom types with isKnownUniquelyReferenced; a copy triggers when a mutation occurs while the buffer has more than one reference. To stay in place, keep a single owner, mutate through inout or directly on a var, call reserveCapacity to avoid reallocation, and avoid passing the array where it gets retained.
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- #swift
- #performance
- #copy-on-write
- #memory
- #optimization
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