go-generics
Use when deciding whether to use Go generics, writing generic functions or types, choosing constraints, or picking between type aliases and type definitions. Also use when a user is writing a utility function that could work with multiple types, even if they don't mention generics explicitly. Does not cover interface design without generics (see go-interfaces).
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Install
Works with every agent the skills CLI supports.
npx skills add https://github.com/cxuu/golang-skills --skill go-generics- 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-generics 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 Generics and Type Parameters
Compatibility: Generics require Go 1.18+.
Resource Routing
references/CONSTRAINTS.md- Read when composing constraints, using type sets, or choosing between generics and interfaces.
When to Use Generics
Start with concrete types. Generalize only when a second type appears.
Prefer Generics When
- Multiple types share identical logic (sorting, filtering, map/reduce)
- You would otherwise rely on
anyand excessive type switching - You are building a reusable data structure (concurrent-safe set, ordered map)
Avoid Generics When
- Only one type is being instantiated in practice
- Interfaces already model the shared behavior cleanly
- The generic code is harder to read than the type-specific alternative
"Write code, don't design types." — Robert Griesemer and Ian Lance Taylor
Decision Flow
Do multiple types share identical logic?
├─ No → Use concrete types
├─ Yes → Do they share a useful interface?
│ ├─ Yes → Use an interface
│ └─ No → Use generics
Bad:
// Premature generics: only ever called with int
func Sum[T constraints.Integer | constraints.Float](vals []T) T {
var total T
for _, v := range vals {
total += v
}
return total
}
Good:
func SumInts(vals []int) int {
var total int
for _, v := range vals {
total += v
}
return total
}
Type Parameter Naming
| Name | Typical Use |
|---|---|
T | General type parameter |
K | Map key type |
V | Map value type |
E | Element/item type |
For complex constraints, a short descriptive name is acceptable:
func Marshal[Opts encoding.MarshalOptions](v any, opts Opts) ([]byte, error)
Type Aliases vs Type Definitions
Type aliases (type Old = new.Name) are rare — use only for package migration
or gradual API refactoring.
Constraint Composition
Combine constraints with ~ (underlying type) and | (union):
type Numeric interface {
~int | ~int8 | ~int16 | ~int32 | ~int64 |
~float32 | ~float64
}
func Sum[T Numeric](vals []T) T {
var total T
for _, v := range vals {
total += v
}
return total
}
Use the constraints package or cmp package (Go 1.21+) for standard constraints
like cmp.Ordered instead of writing your own.
Common Pitfalls
Don't Wrap Standard Library Types
// Bad: generic wrapper adds complexity without value
type Set[T comparable] struct {
m map[T]struct{}
}
// Better: use map[T]struct{} directly when the usage is simple
seen := map[string]struct{}{}
Generics justify their complexity when they eliminate duplication across multiple call sites. A single-use generic is just indirection.
Don't Use Generics for Interface Satisfaction
// Bad: T is only used to satisfy an interface — just use the interface
func Process[T io.Reader](r T) error { ... }
// Good: accept the interface directly
func Process(r io.Reader) error { ... }
Avoid Over-Constraining
// Bad: constraint is more restrictive than needed
func Contains[T interface{ ~int | ~string }](slice []T, target T) bool { ... }
// Good: comparable is sufficient
func Contains[T comparable](slice []T, target T) bool { ... }
Quick Reference
| Topic | Guidance |
|---|---|
| When to use generics | Only when multiple types share identical logic and interfaces don't suffice |
| Starting point | Write concrete code first; generalize later |
| Naming | Single uppercase letter (T, K, V, E) |
| Type aliases | Same type, alternate name; use only for migration |
| Constraint composition | Use ~ for underlying types, ` |
| Common pitfall | Don't genericize single-use code or when interfaces suffice |
Related Skills
- Interfaces vs generics: See go-interfaces when deciding whether an interface already models the shared behavior without generics
- Type declarations: See go-declarations when defining new types, type aliases, or choosing between type definitions and aliases
- Documenting generic APIs: See go-documentation when writing doc comments and runnable examples for generic functions
- Naming type parameters: See go-naming when choosing names for type parameters or constraint interfaces
FAQ
What does the go-generics skill do?
Use when deciding whether to use Go generics, writing generic functions or types, choosing constraints, or picking between type aliases and type definitions. Also use when a user is writing a utility function that could work with multiple types, even if they don't mention generics explicitly. Does not cover interface design without generics (see go-interfaces).
How do I install go-generics?
Run npx skills add https://github.com/cxuu/golang-skills --skill go-generics 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-generics/ (personal) or .claude/skills/go-generics/ (project).
Which AI agents can use go-generics?
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-generics 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-generics?
It is published by cxuu in cxuu/golang-skills. It has 1,017 recorded installs.
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