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Answer: A Go map is a built-in hash table that maps keys to values.

Basics

m := make(map[string]int)
m["route"] = 66
i := m["route"]
n := len(m)
delete(m, "route")   // no-op if missing
i, ok := m["route"] // ok is false if absent

Keys

A key can be any type that supports ==: strings, numbers, booleans, pointers, structs and arrays of comparable types. Slices, maps and functions cannot be keys.

Reference semantics

Maps are reference types, like pointers or slices. Passing a map to a function lets it modify the caller's map. A nil map reads like an empty map, but writing to it panics, so initialize with make.

Iteration

Sort the keys if you need a stable order.

Claims

• id: C1 claim: Go provides a built-in map type that implements a hash table. source: S1 evidence: "Go provides a built-in map type that implements a hash table."
• id: C2 claim: delete does nothing if the key doesn't exist. source: S1 evidence: "will do nothing if the specified key doesn’t exist"
• id: C3 claim: Maps are not safe for concurrent use. source: S1 evidence: "Maps are not safe for concurrent use:"
• id: C4 claim: Map iteration order is not specified. source: S1 evidence: "the iteration order is not specified and is not guaranteed to be the same"
• id: C5 claim: Keys can be any type with an equality operator. source: S2 evidence: "The key can be of any type for which the equality operator is defined,"
• id: C6 claim: Effective Go names the comma ok idiom. source: S2 evidence: "For obvious reasons this is called the “comma ok” idiom."

Sources

• [S1] Go maps in action - The Go Programming Language. The Go Authors (go.dev). https://go.dev/blog/maps . License: CC BY 4.0 (go.dev text). Accessed 2026-11-04.
• [S2] Effective Go - The Go Programming Language. The Go Authors (go.dev). https://go.dev/doc/effective_go . License: CC BY 4.0 (go.dev text). Accessed 2026-11-04.

License: this note is CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Summary by iinventedlight (AI-assisted).

@misc{iil_note_mthw2x6y,
  author = {{iinventedlight}},
  title = {{Go maps}},
  howpublished = {iinventedlight Library},
  year = {2026},
  date = {2026-11-04},
  url = {https://iinventedlight.com/library/notes/go-maps/},
  note = {Permanent ID iil:note:mthw2x6y. License: CC-BY-4.0.},
}

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