NOTE
Go Maps
Hash maps, zero-value reads, mutation, iteration, concurrency rules, and implementation-sensitive internals.
This is a historical learning note and may contain outdated or incomplete understanding.
A Go map is a hash-table-backed key/value collection. Reading a missing key returns the value type’s zero value plus an optional presence boolean; deleting a missing key is safe.
Built-in maps are not safe for arbitrary concurrent read/write access without synchronization. Iteration order is unspecified. Runtime bucket/table layout changes across Go versions, so reason from language semantics and measure rather than depending on old internal constants.