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Answer: A Go array has a fixed length that is part of its type; [4]int and [5]int are different types. A slice is a flexible view onto an underlying array with a length and capacity. Most Go code uses slices, growing them with append.

Arrays

var a [4]int   // zero value: four zeros, ready to use

Arrays are values: assigning or passing one copies all elements.

Slices

s := make([]int, 3, 10) // length 3, capacity 10
s = append(s, 4)
t := s[1:3]             // shares the same backing array

• len(s): number of elements.

Claims

• id: C1 claim: An array's length is part of its type. source: S1 evidence: "An array’s size is fixed; its length is part of its type ([4]int and [5]int"
• id: C2 claim: Unlike an array type, a slice type has no specified length. source: S1 evidence: "Unlike an array type, a slice type has no specified length."
• id: C3 claim: Capacity defaults to the specified length when omitted. source: S1 evidence: "When the capacity argument is omitted, it defaults to the specified length."
• id: C4 claim: Length and capacity are inspected with len and cap. source: S1 evidence: "The length and capacity of a slice can be inspected using the built-in len and"
• id: C5 claim: Slices wrap arrays to give a more convenient interface. source: S2 evidence: "Slices wrap arrays to give a more general, powerful, and convenient"

Sources

• [S1] Go Slices: usage and internals - The Go Programming Language. The Go Authors (go.dev). https://go.dev/blog/slices-intro . 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_vhsx4rga,
  author = {{iinventedlight}},
  title = {{Go slices and arrays}},
  howpublished = {iinventedlight Library},
  year = {2026},
  date = {2026-11-04},
  url = {https://iinventedlight.com/library/notes/go-slices/},
  note = {Permanent ID iil:note:vhsx4rga. License: CC-BY-4.0.},
}

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