When would you use a struct with methods vs a map in Go?

Field names are known at compile time — compile-time typo safety

You need to attach methods and implement interfaces

Performance matters — struct field access is direct memory offset, map access involves hashing

Working with JSON APIs — struct tags control serialization cleanly

You want IDE autocompletion and refactoring support

Keys are only known at runtime (user-supplied, config-driven)

Sparse data where most fields would be zero-valued

Implementing caches, lookup tables, or frequency counters

Processing arbitrary JSON blobs of unknown schema

Building dynamic query parameters or HTTP header collections