# go-dependency-injection

A skill that steers your agent toward constructor injection and a single composition root in main. Useful once globals creep in or tests get hard to write.

- skill · `type=skill` · Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, OpenCode · ★ 83
- Author: eduardo-sl
- License: MIT · policy=mirror · the beginning of the file is at the end of this page
- Source: https://github.com/eduardo-sl/go-agent-skills/tree/HEAD/skills/(architecture)/go-dependency-injection/SKILL.md
- Updated: 2026-10-15
- HTML: https://affpapa.org/en/nevibecode/skills/go-dependency-injection

## What it does

This skill gives the agent a set of rules for wiring dependencies in Go. The default is constructor injection: a service takes its repository, payment gateway and logger as parameters instead of pulling them from package-level variables. All construction happens in one place — `main`, or a `run` function it calls — and the compiler checks the order for you.

There is a section on removing global state, including a migration path for legacy code. You introduce a struct that holds the dependency, leave a deprecated package-level wrapper delegating to one instance built in `main`, move callers across, then delete the wrapper. For narrow seams the skill suggests injecting a function rather than a full interface, like `now func() time.Time`.

On frameworks the stance is blunt: manual wiring holds up longer than people expect, and a hundred-line `run` stays readable. `google/wire` generates the calls at compile time; `uber-go/fx` and `dig` run a container and surface errors at startup. Pick one mechanism — one composition root, no mixing. The Go toolchain is required, while `wire` and `fx` are optional. A project rule or agent config that explicitly supersedes this skill wins.

## Install

### Claude Code (native platform)

1. **Skills CLI (Vercel)**
```bash
npx skills add eduardo-sl/go-agent-skills --skill go-dependency-injection -a claude-code
```

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

### Codex

1. **Skills CLI (Vercel)**
```bash
npx skills add eduardo-sl/go-agent-skills --skill go-dependency-injection -a codex
```

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

### Cursor

1. **Skills CLI (Vercel)**
```bash
npx skills add eduardo-sl/go-agent-skills --skill go-dependency-injection -a cursor
```

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

### GitHub Copilot

1. **GitHub CLI**
```bash
gh skill install eduardo-sl/go-agent-skills go-dependency-injection
```

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

### Gemini CLI

1. **Skills CLI (Vercel)**
```bash
npx skills add eduardo-sl/go-agent-skills --skill go-dependency-injection -a gemini-cli
```

2. **Platform CLI**
```bash
gemini skills install https://github.com/eduardo-sl/go-agent-skills --path 'skills/(architecture)/go-dependency-injection'
```

### Windsurf (Devin Desktop)

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

### OpenCode

**Skills CLI (Vercel)**
```bash
npx skills add eduardo-sl/go-agent-skills --skill go-dependency-injection -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/eduardo-sl/go-agent-skills/tree/HEAD/skills/(architecture)/go-dependency-injection/SKILL.md

## When to use it
- replace a global singleton with an explicit dependency
- gather all wiring into one `main`
- make a component testable without touching process-wide state
- decide between manual wiring and `google/wire`
- move legacy code to constructors without a rewrite

## Example prompts
- Remove the global `var DB` and pass the dependency through the constructor
- Move all wiring into `main`, drop the `init()` calls
- Should I reach for `google/wire` here or keep manual wiring?

## Source text · SKILL.md · MIT

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: 1c56d592c028a8c3.

BEGIN THIRD-PARTY FILE 1c56d592c028a8c3
````text
---
name: go-dependency-injection
description: >
  Dependency injection in Go: constructor injection, wiring in main,
  avoiding global state, and when frameworks (wire, fx, dig) earn their
  complexity. Use when: "dependency injection", "wire up dependencies",
  "inject this", "remove global state", "singleton in Go", "use
  google/wire", "uber fx", "make this testable".
  Not for: interface design (go-interface-design), directory structure
  (go-project-layout), test doubles and mocks (go-test-quality).
user-invocable: true
license: MIT
compatibility: Designed for Claude Code or similar AI coding agents working on Go projects. Requires the Go toolchain. wire and fx are optional.
allowed-tools: Read Edit Write Glob Grep Bash(go:*) Bash(gofmt:*)
metadata:
  author: eduardo-sl
  version: "1.1.2"
---

# Go Dependency Injection

DI in Go is a pattern, not a framework: pass dependencies to
constructors, wire everything explicitly in `main`. Reach for a
framework only when manual wiring measurably hurts.

> Community default. A project skill or agent-config rule that explicitly
> supersedes `go-dependency-injection` takes precedence over this one.

## 1. Constructor Injection — the Default

```go
// ✅ Good — dependencies are explicit parameters
type OrderService struct {
    repo     OrderRepository
    payments PaymentGateway
    logger   *slog.Logger
}

func NewOrderService(repo OrderRepository, payments PaymentGateway, logger *slog.Logger) *OrderService {
    return &OrderService{repo: repo, payments: payments, logger: logger}
}

// ❌ Bad — hidden dependencies reached through globals
func (s *OrderService) Place(ctx context.Context, o Order) error {
    db := database.Get()        // global singleton
    log.Printf("placing order") // global logger
    // untestable without touching process-wide state
}
```

Rules:

- Accept interfaces for dependencies the service calls; return the
  concrete type from the constructor.
- Every dependency visible in the signature — if the list feels long,
  the type does too much (split it), don't hide deps to shorten it.
- Validate required deps in the constructor and return an error
  (or accept a nil-safe default, e.g. `logger = slog.Default()`).

## 2. The Composition Root

All wiring lives in one place — `main` (or a `run` function it calls).
````
END THIRD-PARTY FILE 1c56d592c028a8c3

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