DEV Community: Tetsuro Mikami

Dependency Injection in Go: How Much Is Enough for Web APIs?

Tetsuro Mikami — Wed, 24 Dec 2025 06:50:57 +0000

Dependency Injection (DI) in Go often sparks debates that feel disproportionate to the actual needs of most web APIs. Discussions quickly escalate to containers, lifecycles, scopes, and dynamic resolution—despite the fact that many services have a simple, static dependency graph resolved once at startup.

This article argues a straightforward position:

For a typical web API, compile-time dependency resolution is enough.

From there, we’ll look at why runtime DI frameworks tend to be overkill, why static approaches like wire already cover most needs, and why a field-tag-based generator can simplify things even further.

What most web APIs actually need

If we strip away abstractions, a large percentage of Go web APIs share the same characteristics:

Stateless request handling
Dependencies resolved once at startup
A mostly tree-shaped dependency graph
- config → database → repository → service → handler
No runtime rebinding of implementations

In this environment, DI is not about flexibility at runtime. It’s about wiring correctness and maintainability.

Runtime DI frameworks: powerful, but usually unnecessary

Frameworks such as fx / dig or generics-based containers like do shine when your application behaves like a framework itself:

modules register themselves dynamically
lifecycle hooks (start/stop) matter
plugins or optional components are loaded at runtime

For typical web APIs, however, these features often come with downsides:

additional APIs to learn and remember
runtime error surfaces for what is fundamentally static wiring
harder-to-follow control flow during startup

When dependencies are fixed and known ahead of time, runtime DI solves a problem you don’t really have.

Static wiring is already enough

If dependencies are static, resolving them at compile time or generation time is a natural fit.

This is where tools like wire enter the picture. They provide:

compile-time dependency resolution
no runtime container
plain Go code as output

For a normal web API, this model is already sufficient. You get safety, predictability, and zero runtime DI overhead.

So far, the conclusion is simple:

For most web APIs, static DI is enough.

Where wire starts to feel heavy

Wire’s design emphasizes explicitness:

provider functions
provider sets
injector functions per root

This explicitness can be valuable in some organizational contexts. But in day-to-day API development, it often turns into maintenance overhead:

provider sets need constant updates as the graph evolves
DI-specific files grow alongside business code
the wiring itself becomes something developers have to reason about

The static model is right—but the amount of ceremony is not always justified.

A lighter static model: field-tag-based generation

If your goal is still static wiring and generated constructors, but with less DI-specific code, a simpler model works well:

declare what you want in a container struct
let a generator resolve the graph
emit plain Go constructors

Conceptually:

type Container struct {
    Handler *UserHandler `inject:""`
}

The generated code is just Go:

func NewContainer() (*Container, error) {
    cfg := NewConfig()
    db, err := NewDatabase(cfg)
    if err != nil {
        return nil, err
    }
    svc := NewUserService(db)
    h := NewUserHandler(svc)
    return &Container{Handler: h}, nil
}

No runtime container. No provider sets. No reflection.

This is the idea behind injector, a field-tag-only DI code generator:

https://github.com/mickamy/injector

The link is intentionally placed here, after the argument is established, rather than as an upfront pitch.

Is there still a place for wire?

Wire can still make sense when:

provider sets are treated as a public composition API
explicit wiring boundaries are a deliberate design goal
DI graphs are reviewed and curated as first-class artifacts

In other words, wire’s strengths are organizational and process-driven.

If your project doesn’t need that level of explicitness, wire becomes harder to justify.

Practical takeaway

Runtime DI (fx/dig, do)
- Powerful, but often overkill for standard web APIs
Static DI (wire)
- Sufficient for most APIs, but verbose
Static + minimal (injector)
- Same guarantees, less ceremony

For the common case—stateless web APIs with stable dependency graphs—static wiring is enough.

And if you can keep that wiring static and reduce the amount of DI-specific code you maintain, that’s an even better outcome.

Closing

Dependency Injection doesn’t need to be a framework-level decision for most Go web APIs. It’s a startup detail.

Resolve dependencies once. Generate plain Go code. Keep the wiring boring.

If wire already feels sufficient—but a bit heavy—the field-tag-based approach is a natural next step.

In that sense, injector is not a radical alternative.

It’s simply asking:

If static DI is enough… why not make it simpler?

Dependency Injection in Go, Reduced to Field Tags

Tetsuro Mikami — Thu, 18 Dec 2025 01:47:08 +0000

Dependency Injection (DI) in Go often feels heavier than it should be.

Once a project grows, you start seeing patterns like:

Large provider sets
Dedicated wiring files (for tools like wire)
Initialization order that humans must carefully maintain
DI-specific code spreading across the codebase

Over time, the amount of code written for DI itself can rival the actual business logic.

I wanted to see how far DI could be simplified in Go.

That experiment became injector.

The Core Idea

All dependency injection is declared using struct field tags.

Nothing else.

No provider sets.
No DSL.
No runtime reflection.

The container declares what is injected.
Providers declare how values are constructed.

The Container

A container is just a struct. Fields marked with the inject tag are managed by injector.

type Container struct {
    UserService service.UserService `inject:""`
}

The inject tag is intentionally minimal:

It is a marker only
It carries no configuration by default
It simply means “this field is injected by injector”

Providers

A provider is any top-level function that returns a value.

func NewUserService(db infra.Database) service.UserService {
    return &userService{DB: db}
}

Rules are simple:

The function must be top-level (no receiver)
Parameters are dependencies
The return value is the provided type

Injector discovers providers automatically via static analysis.

Generated Code

Running the generator:

injector generate ./...

Produces plain Go code:

func NewContainer() *Container {
    cfg := NewDatabaseConfig()
    db := NewDatabase(cfg)
    user := NewUserService(db)

    return &Container{
        UserService: user,
    }
}

There is no runtime magic.
The generated code is readable, debuggable, and type-safe.

Interface-First by Default

Injector works naturally with interfaces.

type UserService interface {
    Register(name, password string) error
}

func NewUserService(db infra.Database) UserService {
    return &userService{DB: db}
}

The container exposes only interfaces.
Concrete implementations remain private.

This keeps application boundaries clean without adding DI-specific abstractions.

Handling Multiple Providers

If multiple providers return the same type, injector requires an explicit choice.

type Container struct {
    _ config.DatabaseConfig `inject:"provider:NewPrimaryDatabaseConfig"`
    UserService service.UserService `inject`
}

A blank (_) field:

Does not expose the dependency
Declares a provider override
Applies globally within the container

Provider selection remains centralized and explicit.

Why Field Tags?

Go structs already represent dependency lists.

Adding extra configuration layers often makes DI harder to reason about, not easier.

By limiting DI declarations to field tags:

Dependencies are visible at a glance
Configuration stays local
The mental model stays small

DI should be infrastructure, not the focus of the codebase.

Status

Injector is intentionally small and opinionated.

The current goal is not feature breadth, but clarity:

Marker-based containers
Provider-based resolution
Compile-time dependency graphs

Future ideas exist, but they can wait until real-world usage drives them.