Go: What is the difference between map and struct?

Map — dynamic, runtime-checked key-value store. Struct — static, compile-time-checked collection of named fields.

Maps are ideal when the set of keys isn't known at compile time. They use hash tables internally, giving O(1) average-case lookups. Maps are reference types — passing one to a function shares the same underlying data.

1headers := make(map[string]string)
2for _, h := range rawHeaders {
3    key, val := strings.SplitN(h, ":", 2)
4    headers[strings.TrimSpace(key)] = strings.TrimSpace(val)
5}

Structs define a fixed schema the compiler knows about. This enables IDE support, catches errors early, and makes the code self-documenting. Structs compose cleanly via embedding.

1type HTTPRequest struct {
2    Method  string            `json:"method"`
3    URL     string            `json:"url"`
4    Headers map[string]string `json:"headers"`
5}

When to use:

• Map — dynamic keys, caching, grouping, counting, configuration.
• Struct — domain models, API payloads, any fixed-shape data.

Common mistakes:

• Using map[string]interface{} instead of proper structs — lose type safety.
• Reading maps without checking ok — zero value silently returned.
• Concurrent map writes without synchronization — runtime panic.
• Forgetting maps can't be compared with == (except nil check).