sync.Map

Canonical guidance

• prefer map plus mutex by default
• use sync.Map for its intended concurrent access patterns
• keep the untyped boundary small

Use when

• read-mostly caches
• keys written once then read many times
• concurrent access patterns with disjoint key sets

Avoid

• reaching for sync.Map as the default concurrent map
• spreading any type assertions everywhere
• assuming sync.Map is automatically faster

Preferred pattern

var cache sync.Map
cache.Store(key, value)
v, ok := cache.Load(key)

Anti-pattern

• replacing a small, easy-to-lock map with sync.Map because “concurrent data needs a concurrent container”

Explanation: This anti-pattern is tempting because the API looks purpose-built, but it often makes simple state harder to understand and type-check.

Why

• sync.Map is specialized, not a general replacement for ordinary map ownership