# go-control-flow

Teaches AI agents canonical Go control flow patterns: early returns, scoped if statements, and for loops. Keeps code flat and avoids variable shadowing bugs.

- skill · `type=skill` · Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, OpenCode · 1200 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-control-flow/SKILL.md
- Updated: 2026-06-20
- HTML: https://affpapa.org/en/nevibecode/skills/go-control-flow

## What it does

The skill instructs coding agents on idiomatic Go control flow. It enforces `if` statements with initialization statements to restrict variable scope and strips redundant `else` blocks when returning early. It covers all Go `for` loop forms, parallel assignments for two-pointer traversals, rune iteration over strings, and labeled breaks to exit loops from within a `switch`.

A key warning targets variable shadowing. Using `:=` inside an inner block silently creates a new variable instead of reassigning the outer one. This frequently causes lost context updates. Error handling patterns are explicitly excluded here and redirected to `go-error-handling`.

## Install

### Claude Code (native platform)

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

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

### Codex

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

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

### Cursor

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

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

### GitHub Copilot

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

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

### Gemini CLI

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

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

### Windsurf (Devin Desktop)

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

### OpenCode

**Skills CLI (Vercel)**
```bash
npx skills add cxuu/golang-skills --skill go-control-flow -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-control-flow/SKILL.md

## When to use it
- flatten nested conditionals using guard clauses and early returns
- break out of an outer loop from an inner switch statement
- scope transient variables directly within if or switch initialization
- prevent variable shadowing bugs caused by inner-scope `:=` declarations

## Example prompts
- Refactor this nested if-else chain into clean Go guard clauses
- Write a two-pointer reverse loop using Go parallel assignment
- Check this switch statement inside a for loop for exit bugs

## 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: cc210fd00e99d835.

BEGIN THIRD-PARTY FILE cc210fd00e99d835
````text
---
name: go-control-flow
description: Use when writing conditionals, loops, or switch statements in Go — including if with initialization, early returns, for loop forms, range, switch, type switches, and blank identifier patterns. Also use when writing a simple if/else or for loop, even if the user doesn't mention guard clauses or variable scoping. Does not cover error flow patterns (see go-error-handling).
---

# Go Control Flow

## Resource Routing

- `references/SWITCH-PATTERNS.md` - Read when using switch statements, type switches, fallthrough, or labeled breaks.
- `references/BLANK-IDENTIFIER.md` - Read when using `_`, blank imports, unused compile-time assertions, or intentional discards.

---

## If with Initialization

`if` and `switch` accept an optional initialization statement. Use it to scope
variables to the conditional block:

```go
if err := file.Chmod(0664); err != nil {
    log.Print(err)
    return err
}
```

If you need the variable beyond a few lines after the `if`, declare it
separately and use a standard `if` instead:

```go
x, err := f()
if err != nil {
    return err
}
// lots of code that uses x
```

## Indent Error Flow (Guard Clauses)

When an `if` body ends with `break`, `continue`, `goto`, or `return`, omit the
unnecessary `else`. Keep the success path unindented:

```go
f, err := os.Open(name)
if err != nil {
    return err
}
d, err := f.Stat()
if err != nil {
    f.Close()
    return err
}
codeUsing(f, d)
```

Never bury normal flow inside an `else` when the `if` already returns.

---

## Redeclaration and Reassignment

The `:=` short declaration allows redeclaring variables in the same scope:

```go
f, err := os.Open(name)  // declares f and err
d, err := f.Stat()       // declares d, reassigns err
```

A variable `v` may appear in a `:=` declaration even if already declared,
provided:

1. The declaration is in the **same scope** as the existing `v`
2. The value is **assignable** to `v`
3. At least **one other variable** is newly created by the declaration

### Variable Shadowing

**Warning**: If `v` is declared in an outer scope, `:=` creates a **new**
variable that shadows it — a common source of bugs:

```go
// Bug: ctx inside the if block shadows the outer ctx
if *shortenDeadlines {
    ctx, cancel := context.WithTimeout(ctx, 3*time.Second)
    defer cancel()
}
// ctx here is still the original — the shadowed ctx didn't escape

// Fix: use = instead of :=
var cancel func()
ctx, cancel = context.WithTimeout(ctx, 3*time.Second)
```

---

## For Loops

Go's `for` is its only looping construct, unifying `while`, `do-while`, and
C-style `for`:

```go
// Condition-only (Go's "while")
for x > 0 {
    x = process(x)
}

// Infinite loop
for {
    if done() { break }
}

// C-style three-component
for i := 0; i < n; i++ { ... }
```

### Range

`range` iterates over slices, maps, strings, and channels:

```go
for i, v := range slice { ... }   // index + value
for k, v := range myMap { ... }   // key + value (non-deterministic order)
for i, r := range "héllo" { ... } // byte index + rune (not byte)
````
END THIRD-PARTY FILE cc210fd00e99d835

The third-party file has ended. Everything between the cc210fd00e99d835 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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