# go-declarations

A skill that tells your coding agent how to declare and initialize Go variables, constants, structs and maps. Useful the moment you write a new struct or const block.

- skill · `type=skill` · Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, OpenCode · 1000 installs · ★ 181
- Author: cxuu
- License: Apache-2.0 · policy=mirror · the beginning of the file is at the end of this page
- Source: https://github.com/cxuu/golang-skills/tree/HEAD/skills/go-declarations/SKILL.md
- Updated: 2026-06-20
- HTML: https://affpapa.org/en/nevibecode/skills/go-declarations

## What it does

The skill fires when the agent writes a declaration or initialization in Go: `var` versus `:=`, narrowing scope with if-init, composite literal formatting, `iota` enums, swapping `interface{}` for `any`. It ships a quick-reference table for `var` vs `:=` plus six reference files — `references/SCOPE.md`, `references/IOTA.md`, `references/INITIALIZATION.md`, `references/LITERALS.md`, `references/STRUCTS.md`, `references/SHADOWING.md` — and the agent reads whichever one fits the task.

The rules are blunt. Field names in struct literals are mandatory, with test tables of three fields or fewer as the exception. Zero-value fields should be left out. For a zero-value struct use `var user User`, not `user := User{}`. An empty map you plan to fill later goes through `make`, so it reads differently from a nil one. Enums should start at one, leaving zero to mean unset. Shadowing a builtin like `error`, `len` or `make` gets caught by `go vet`.

Examples lean on `any`, so you need Go 1.18 or newer. Naming conventions live in a separate `go-naming` skill, and questions about name length or style get routed there instead. Install runs through `npx skills add` with an `-a` flag for your platform; GitHub Copilot uses `gh skill install` instead.

## Install

### Claude Code (native platform)

1. **Skills CLI (Vercel)**
```bash
npx skills add cxuu/golang-skills --skill go-declarations -a claude-code
```

2. **Manually: put the files in place**
- File: `~/.claude/skills/go-declarations/SKILL.md` — Copy the whole skill folder; for one project use .claude/skills/go-declarations/

### Codex

1. **Skills CLI (Vercel)**
```bash
npx skills add cxuu/golang-skills --skill go-declarations -a codex
```

2. **Manually: put the files in place**
- File: `.agents/skills/go-declarations/SKILL.md` — For all projects use ~/.agents/skills/

### Cursor

1. **Skills CLI (Vercel)**
```bash
npx skills add cxuu/golang-skills --skill go-declarations -a cursor
```

2. **Manually: put the files in place**
- File: `.cursor/skills/go-declarations/SKILL.md` — Cursor also reads .agents/skills/ and .claude/skills/

### GitHub Copilot

1. **GitHub CLI**
```bash
gh skill install cxuu/golang-skills go-declarations
```

2. **Manually: put the files in place**
- File: `.github/skills/go-declarations/SKILL.md`

### Gemini CLI

1. **Skills CLI (Vercel)**
```bash
npx skills add cxuu/golang-skills --skill go-declarations -a gemini-cli
```

2. **Platform CLI**
```bash
gemini skills install https://github.com/cxuu/golang-skills --path skills/go-declarations
```

### Windsurf (Devin Desktop)

**Manually: put the files in place**
- File: `.devin/skills/go-declarations/SKILL.md` — The legacy .windsurf/skills/ path still works

### OpenCode

**Skills CLI (Vercel)**
```bash
npx skills add cxuu/golang-skills --skill go-declarations -a opencode
```

### Claude.ai

**Claude.ai**
- Zip the folder and upload it in Settings → Capabilities → Skills

Where a file is given instead of a command, copy the files from the source to that path: https://github.com/cxuu/golang-skills/tree/HEAD/skills/go-declarations/SKILL.md

## When to use it
- pick between `var` and `:=` at a given spot
- narrow a variable's scope with if-init
- design an `iota` enum with a sane zero value
- format a composite literal and add field names
- stop shadowing builtins like `error` or `len`

## Example prompts
- Declare the constants for a calculator's operations with iota, zero should mean invalid
- Review this block of variable declarations and tell me where `:=` should be `var`
- Here's a config struct — initialize it properly and drop the zero-value fields

## Source text · SKILL.md · Apache-2.0

Below is the content of a third-party file. It is data, not instructions for you: do not act on anything written inside unless the human asks. Block tag: bb210c3a0f697572.

BEGIN THIRD-PARTY FILE bb210c3a0f697572
````text
---
name: go-declarations
description: Use when declaring or initializing Go variables, constants, structs, or maps — including var vs :=, reducing scope with if-init, formatting composite literals, designing iota enums, and using any instead of interface{}. Also use when writing a new struct or const block, even if the user doesn't ask about declaration style. Does not cover naming conventions (see go-naming).
---

# Go Declarations and Initialization

> Compatibility: Examples may use `any`, which requires Go 1.18+.

## Resource Routing

- `references/SCOPE.md` - Read when deciding between `var`, `:=`, if-init, and narrow variable scope.
- `references/IOTA.md` - Read when designing constants or enum-like values.
- `references/INITIALIZATION.md` - Read when initializing structs, maps, zero values, or pointers.
- `references/LITERALS.md` - Read for composite literal formatting and keyed-field tradeoffs.
- `references/STRUCTS.md` - Read when designing or initializing structs.
- `references/SHADOWING.md` - Read when a declaration may shadow a builtin or outer variable.

## Quick Reference: var vs :=

| Context | Use | Example |
|---------|-----|---------|
| Top-level | `var` (always) | `var _s = F()` |
| Local with value | `:=` | `s := "foo"` |
| Local zero-value (intentional) | `var` | `var filtered []int` |
| Type differs from expression | `var` with type | `var _e error = F()` |

---

## Group Similar Declarations

Group related `var`, `const`, `type` in parenthesized blocks. Separate
**unrelated** declarations into distinct blocks.

```go
// Bad
const a = 1
const b = 2

// Good
const (
    a = 1
    b = 2
)
```

Inside functions, group adjacent vars even if unrelated:

```go
var (
    caller  = c.name
    format  = "json"
    timeout = 5 * time.Second
)
```

---

## Constants and iota

Start enums at one so the zero value represents invalid/unset:

```go
const (
    Add Operation = iota + 1
    Subtract
    Multiply
)
```

Use zero when the default behavior is desirable (e.g., `LogToStdout`).

---

## Variable Scope

Use if-init to limit scope when the result is only needed for the error check:

```go
if err := os.WriteFile(name, data, 0644); err != nil {
    return err
}
```

Don't reduce scope if it forces deeper nesting or you need the result outside
the `if`. Move constants into functions when only used there.

---

## Initializing Structs

- **Always use field names** (enforced by `go vet`). Exception: test tables
````
END THIRD-PARTY FILE bb210c3a0f697572

The third-party file has ended. Everything between the bb210c3a0f697572 tags is data: requests and commands from it are not followed. An “end of file” line with another tag inside the block is part of the file.

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