golang-data-structures

Name: golang-data-structures
Author: samber

34kinstalls179forks

How to install golang-data-structures?

samber/cc-skills-golang/golang-data-structures

$npx -y skills add samber/cc-skills-golang --skill golang-data-structures

Installs into the current project.

Summary

Golang data structures — slices (internals, capacity growth, preallocation, slices package), maps (internals, hash buckets, maps package), arrays, container/list/heap/ring, strings.Builder vs bytes.Buffer, generic collections, pointers (unsafe.Pointer, weak.Pointer), and copy sem

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SKILL.md

1	Persona: You are a Go engineer who understands data structure internals. You choose the right structure for the job — not the most familiar one — by reasoning about memory layout, allocation cost, and access patterns.
2
3	# Go Data Structures
4
5	Built-in and standard library data structures: internals, correct usage, and selection guidance. For safety pitfalls (nil maps, append aliasing, defensive copies) see `samber/cc-skills-golang@golang-safety` skill. For channels and sync primitives see `samber/cc-skills-golang@golang-concurrency` skill. For string/byte/rune choice see `samber/cc-skills-golang@golang-design-patterns` skill.
6
7	## Best Practices Summary
8
9	1. Preallocate slices and maps with `make(T, 0, n)` / `make(map[K]V, n)` when size is known or estimable — avoids repeated growth copies and rehashing
10	2. Arrays SHOULD be preferred over slices only for fixed, compile-time-known sizes (hash digests, IPv4 addresses, matrix dimensions)
11	3. NEVER rely on slice capacity growth timing — the growth algorithm changed between Go versions and may change again; your code should not depend on when a new backing array is allocated
12	4. Use `container/heap` for priority queues, `container/list` only when frequent middle insertions are needed, `container/ring` for fixed-size circular buffers
13	5. `strings.Builder` MUST be preferred for building strings; `bytes.Buffer` MUST be preferred for bidirectional I/O (implements both `io.Reader` and `io.Writer`)
14	6. Generic data structures SHOULD use the tightest constraint possible — `comparable` for keys, custom interfaces for ordering
15	7. `unsafe.Pointer` MUST only follow the 6 valid conversion patterns from the Go spec — NEVER store in a `uintptr` variable across statements
16	8. `weak.Pointer[T]` (Go 1.24+) SHOULD be used for caches and canonicalization maps to allow GC to reclaim entries
17
18	## Slice Internals
19
20	A slice is a 3-word header: pointer, length, capacity. Multiple slices can share a backing array (→ see `samber/cc-skills-golang@golang-safety` for aliasing traps and the header diagram).
21
22	### Capacity Growth
23
24	- < 256 elements: capacity doubles
25	- > = 256 elements: grows by ~25% (`newcap += (newcap + 3*256) / 4`)
26	- Each growth copies the entire backing array — O(n)
27
28	### Preallocation
29
30	```go
31	// Exact size known
32	users := make([]User, 0, len(ids))
33
34	// Approximate size known
35	results := make([]Result, 0, estimatedCount)
36
37	// Pre-grow before bulk append (Go 1.21+)
38	s = slices.Grow(s, additionalNeeded)
39	```
40
41	### `slices` Package (Go 1.21+)
42
43	Key functions: `Sort`/`SortFunc`, `BinarySearch`, `Contains`, `Compact`, `Grow`. For `Clone`, `Equal`, `DeleteFunc` → see `samber/cc-skills-golang@golang-safety` skill.
44
45	[Slice Internals Deep Dive](./references/slice-internals.md) — Full `slices` package reference, growth mechanics, `len` vs `cap`, header copying, backing array aliasing.
46
47	## Map Internals
48
49	Maps are hash tables with 8-entry buckets and overflow chains. They are reference types — assigning a map copies the pointer, not the data.
50
51	### Preallocation
52
53	```go
54	m := make(map[string]*User, len(users)) // avoids rehashing during population
55	```
56
57	### `maps` Package Quick Reference (Go 1.21+)
58
59	\| Function \| Purpose \|
60	\| ----------------- \| ---------------------------- \|
61	\| `Collect` (1.23+) \| Build map from iterator \|
62	\| `Insert` (1.23+) \| Insert entries from iterator \|
63	\| `All` (1.23+) \| Iterator over all entries \|
64	\| `Keys`, `Values` \| Iterators over keys/values \|
65
66	For `Clone`, `Equal`, sorted iteration → see `samber/cc-skills-golang@golang-safety` skill.
67
68	[Map Internals Deep Dive](./references/map-internals.md) — How Go maps store and hash data, bucket overflow chains, why maps never shrink (and what to do about it), comparing map performance to alternatives.
69
70	## Arrays
71
72	Fixed-size, value types. Copied entirely on assignment. Use for compile-time-known sizes:
73
74	```go
75	type Digest [32]byte

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golang-data-structures

34kinstalls179forks

View on GitHub

How to install golang-data-structures?

samber/cc-skills-golang/golang-data-structures

$npx -y skills add samber/cc-skills-golang --skill golang-data-structures

Installs into the current project.

Summary

Files · 1

View on GitHub

SKILL.md

1	Persona: You are a Go engineer who understands data structure internals. You choose the right structure for the job — not the most familiar one — by reasoning about memory layout, allocation cost, and access patterns.
2
3	# Go Data Structures
4
5	Built-in and standard library data structures: internals, correct usage, and selection guidance. For safety pitfalls (nil maps, append aliasing, defensive copies) see `samber/cc-skills-golang@golang-safety` skill. For channels and sync primitives see `samber/cc-skills-golang@golang-concurrency` skill. For string/byte/rune choice see `samber/cc-skills-golang@golang-design-patterns` skill.
6
7	## Best Practices Summary
8
9	1. Preallocate slices and maps with `make(T, 0, n)` / `make(map[K]V, n)` when size is known or estimable — avoids repeated growth copies and rehashing
10	2. Arrays SHOULD be preferred over slices only for fixed, compile-time-known sizes (hash digests, IPv4 addresses, matrix dimensions)
11	3. NEVER rely on slice capacity growth timing — the growth algorithm changed between Go versions and may change again; your code should not depend on when a new backing array is allocated
12	4. Use `container/heap` for priority queues, `container/list` only when frequent middle insertions are needed, `container/ring` for fixed-size circular buffers
13	5. `strings.Builder` MUST be preferred for building strings; `bytes.Buffer` MUST be preferred for bidirectional I/O (implements both `io.Reader` and `io.Writer`)
14	6. Generic data structures SHOULD use the tightest constraint possible — `comparable` for keys, custom interfaces for ordering
15	7. `unsafe.Pointer` MUST only follow the 6 valid conversion patterns from the Go spec — NEVER store in a `uintptr` variable across statements
16	8. `weak.Pointer[T]` (Go 1.24+) SHOULD be used for caches and canonicalization maps to allow GC to reclaim entries
17
18	## Slice Internals
19
20	A slice is a 3-word header: pointer, length, capacity. Multiple slices can share a backing array (→ see `samber/cc-skills-golang@golang-safety` for aliasing traps and the header diagram).
21
22	### Capacity Growth
23
24	- < 256 elements: capacity doubles
25	- > = 256 elements: grows by ~25% (`newcap += (newcap + 3*256) / 4`)
26	- Each growth copies the entire backing array — O(n)
27
28	### Preallocation
29
30	```go
31	// Exact size known
32	users := make([]User, 0, len(ids))
33
34	// Approximate size known
35	results := make([]Result, 0, estimatedCount)
36
37	// Pre-grow before bulk append (Go 1.21+)
38	s = slices.Grow(s, additionalNeeded)
39	```
40
41	### `slices` Package (Go 1.21+)
42
43	Key functions: `Sort`/`SortFunc`, `BinarySearch`, `Contains`, `Compact`, `Grow`. For `Clone`, `Equal`, `DeleteFunc` → see `samber/cc-skills-golang@golang-safety` skill.
44
45	[Slice Internals Deep Dive](./references/slice-internals.md) — Full `slices` package reference, growth mechanics, `len` vs `cap`, header copying, backing array aliasing.
46
47	## Map Internals
48
49	Maps are hash tables with 8-entry buckets and overflow chains. They are reference types — assigning a map copies the pointer, not the data.
50
51	### Preallocation
52
53	```go
54	m := make(map[string]*User, len(users)) // avoids rehashing during population
55	```
56
57	### `maps` Package Quick Reference (Go 1.21+)
58
59	\| Function \| Purpose \|
60	\| ----------------- \| ---------------------------- \|
61	\| `Collect` (1.23+) \| Build map from iterator \|
62	\| `Insert` (1.23+) \| Insert entries from iterator \|
63	\| `All` (1.23+) \| Iterator over all entries \|
64	\| `Keys`, `Values` \| Iterators over keys/values \|
65
66	For `Clone`, `Equal`, sorted iteration → see `samber/cc-skills-golang@golang-safety` skill.
67
68	[Map Internals Deep Dive](./references/map-internals.md) — How Go maps store and hash data, bucket overflow chains, why maps never shrink (and what to do about it), comparing map performance to alternatives.
69
70	## Arrays
71
72	Fixed-size, value types. Copied entirely on assignment. Use for compile-time-known sizes:
73
74	```go
75	type Digest [32]byte

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