go-data-structures
Use when working with Go slices, maps, or arrays — choosing between new and make, using append, declaring empty slices (nil vs literal for JSON), implementing sets with maps, and copying data at boundaries. Also use when building or manipulating collections, even if the user doesn't ask about allocation idioms. Does not cover concurrent data structure safety (see go-concurrency).
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Install
Works with every agent the skills CLI supports.
npx skills add https://github.com/cxuu/golang-skills --skill go-data-structures- 01
Install
Run the command in your project. The CLI asks which agents to install for.
- 02
Describe the task
Ask your agent for something this skill covers. It loads go-data-structures automatically when relevant.
- 03
Review the result
The agent follows the SKILL.md steps, scripts and references bundled with the skill.
SKILL.md
The instructions your agent reads when the skill is triggered.
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.
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.
When designing interfaces, avoid distinguishing between nil and non-nil zero-length slices.
Maps
Implementing a Set
Use map[T]struct{} when the map is only a set. The empty struct takes no
storage and makes membership intent explicit:
attended := map[string]struct{}{"Ann": {}, "Joe": {}}
if _, ok := attended[person]; ok {
fmt.Println(person, "was at the meeting")
}
Use boolean map values only when the value carries a separate meaning beyond presence.
Copying
Be careful when copying a struct from another package. If the type has methods
on its pointer type (*T), copying the value can cause aliasing bugs.
General rule: Do not copy a value of type T if its methods are associated
with the pointer type *T. This applies to bytes.Buffer, sync.Mutex,
sync.WaitGroup, and types containing them.
// Bad: copying a mutex
var mu sync.Mutex
mu2 := mu // almost always a bug
// Good: pass by pointer
func increment(sc *SafeCounter) {
sc.mu.Lock()
sc.count++
sc.mu.Unlock()
}
Quick Reference
| Topic | Key Point |
|---|---|
| Slices | Always assign append result; nil slice preferred over []T{} |
| Sets | map[T]struct{} for membership-only sets |
| Copying | Don't copy T if methods are on *T; beware aliasing |
Related Skills
- Defensive copying: See go-defensive when copying slices or maps at API boundaries to prevent mutation
- Capacity hints: See go-performance when pre-sizing slices or maps for known workloads
- Iteration patterns: See go-control-flow when using range loops over slices, maps, or channels
- Declaration style: See go-declarations when choosing between
new,make,var, and composite literals
FAQ
What does the go-data-structures skill do?
Use when working with Go slices, maps, or arrays — choosing between new and make, using append, declaring empty slices (nil vs literal for JSON), implementing sets with maps, and copying data at boundaries. Also use when building or manipulating collections, even if the user doesn't ask about allocation idioms. Does not cover concurrent data structure safety (see go-concurrency).
How do I install go-data-structures?
Run npx skills add https://github.com/cxuu/golang-skills --skill go-data-structures in your project. The skills CLI detects the agents you use and copies the skill into the right folder. For Claude Code you can also place the skill folder at ~/.claude/skills/go-data-structures/ (personal) or .claude/skills/go-data-structures/ (project).
Which AI agents can use go-data-structures?
Any agent that supports the open Agent Skills format (a folder with a SKILL.md file), including Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, Windsurf, Cline, OpenCode and more.
Is go-data-structures safe to install?
No partner security audit is available yet. Skills can run commands and scripts, so read the SKILL.md and any bundled files before installing.
Who maintains go-data-structures?
It is published by cxuu in cxuu/golang-skills. It has 1,206 recorded installs.
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