Fix go-cannot-assign-to: Cannot assign to struct field in map or range variable

Wed, 01 Jul 2026 11:17:00 +0800

1. Symptoms

The go-cannot-assign-to error manifests during compilation when attempting to modify struct fields obtained from map indexing or range iteration. The Go compiler emits messages like:

./main.go:15:9: cannot assign to struct field user.Name in map
./main.go:20:12: cannot assign to struct field item.Value in range iterate variable

Typical shell output from go build or go run halts with exit code 1, preventing execution. Indicators include failed builds in CI/CD pipelines, IDE red squiggles under assignment operators (=), and hover tooltips citing “non-name” or “cannot assign to” for expressions like m[key].Field = newValue or for _, v := range slice { v.Field = updated }. This error blocks code that iterates over collections intending to mutate elements, common in data processing, configuration updates, or graph traversals. No runtime symptoms occur since compilation fails outright.

Pointers on ErrorVault — Developer Error Code Dictionary

Fix go-cannot-assign-to: Cannot assign to struct field in map or range variable

1. Symptoms