Go: What is the difference between map and struct?

Map — dynamic key-value store with O(1) lookups, reference type. Struct — fixed set of named, typed fields, compile-time checked, value type.

Maps are reference types — all copies point to the same underlying data. They grow dynamically but are not safe for concurrent writes without synchronization. Keys must be comparable.

1ages := map[string]int{
2    "Alice": 30,
3    "Bob":   25,
4}
5ages["Charlie"] = 35   // add
6delete(ages, "Bob")    // remove
7v, ok := ages["Alice"] // safe lookup

Structs define a fixed schema at compile time. The compiler catches type errors and typos. Structs are value types and compose via embedding.

1type Person struct {
2    Name string
3    Age  int
4}
5p := Person{Name: "Alice", Age: 30}
6p.Age = 31  // compile-time safe

When to use:

• Map — dynamic keys, caching, configuration, grouping.
• Struct — known-shape data, domain models, configs.

Common mistakes:

• Using map[string]interface{} for everything — lose type safety.
• Accessing a map key without checking ok — silently returns zero value.
• Concurrent map writes cause runtime panic — use sync.Map or mutex.
• Comparing maps with == — only valid against nil.