go-data-structures

Go Data Structures

Resource Routing

• references/SLICES.md - Read when deciding nil versus empty slices, copying slices, or managing slice capacity and aliasing.

Choosing a Data Structure

What do you need?
├─ Ordered collection of items
│  ├─ Fixed size known at compile time → Array [N]T
│  └─ Dynamic size → Slice []T
│     ├─ Know approximate size? → make([]T, 0, capacity)
│     └─ Unknown size or nil-safe for JSON? → var s []T (nil)
├─ Key-value lookup
│  └─ Map map[K]V
│     ├─ Know approximate size? → make(map[K]V, capacity)
│     └─ Need a set? → map[T]struct{} (zero-size values)
└─ Need to pass to a function?
   └─ Copy at the boundary if the caller might mutate it

When this skill does NOT apply: For concurrent access to data structures (mutexes, atomic operations), see go-concurrency. For defensive copying at API boundaries, see go-defensive. For pre-sizing capacity for performance, see go-performance.

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Slices

The append Function

Always assign the result — the underlying array may change:

x := []int{1, 2, 3}
x = append(x, 4, 5, 6)

// Append a slice to a slice
x = append(x, y...)  // Note the ...

Two-Dimensional Slices

Independent inner slices (can grow/shrink independently):

picture := make([][]uint8, YSize)
for i := range picture {
    picture[i] = make([]uint8, XSize)
}

Single allocation (more efficient for fixed sizes):

picture := make([][]uint8, YSize)
pixels := make([]uint8, XSize*YSize)
for i := range picture {
    picture[i], pixels = pixels[:XSize], pixels[XSize:]
}

Declaring Empty Slices

Prefer nil slices over empty literals:

// Good: nil slice
var t []string

// Avoid: non-nil but zero-length
t := []string{}

Both have len and cap of zero, but the nil slice is the preferred style.

Exception for JSON: A nil slice encodes to null, while []string{} encodes to []. Use non-nil when you need a JSON array.