Go quirks: function closures capturing mutable references

5 hours ago

Function closures in Go capture variables by reference, allowing them to see future writes to mutable data, which can lead to bugs if not handled carefully.
Closures capturing pointers or mutable structs can cause data races, especially in concurrent code, as they share state with the original variable.
To avoid issues, prefer capturing immutable values (e.g., strings, ints) or create snapshots of mutable data by copying values into local variables before closure creation.
Method values in Go capture their receiver by reference, meaning they read live state from the receiver each time they are called.
Go 1.22 changed loop-variable capture behavior to provide each iteration with its own copy, but pointer captures and method values on long-lived receivers still capture by reference.
Tools like `go test -race` and `go vet`'s loopclosure checker can help detect some race conditions and loop-variable issues, but they may not catch all pitfalls.
When closures need live state, use synchronization mechanisms like mutexes or atomic operations to ensure safe access, and document shared fields clearly.

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