Difference Between `any` and `interface{}` Usage Patterns in Go

any is a built-in type alias for interface{} introduced in Go 1.18 that produces identical compiled output but signals modern, generic-friendly code, whereas interface{} should be reserved for legacy contexts and non-generic APIs.

The JetBrains/go-modern-guidelines repository establishes clear conventions for adopting post-generics Go idioms. While any and interface{} are functionally equivalent at the compiler level, they convey distinct semantic intentions that affect readability, maintenance, and type system design.

Functional Equivalence and Historical Context

Both any and interface{} represent the empty interface type, meaning they can hold values of any concrete type. The critical distinction lies in their introduction timeline and intended usage patterns.

interface{} has been part of Go since its inception, serving as the language's universal container. any was added as a predeclared alias in Go 1.18 alongside generics support. According to the source code analysis in FEATURES.md, this addition was specifically designed to provide clearer syntax for unconstrained type parameters.

Despite being separate identifiers, they compile to identical underlying types with zero performance difference.

Generics Constraints and Type Parameters

The most significant technical divergence appears in generic programming contexts. As documented in [FEATURES.md at line 1808](https://github.com/JetBrains/go-modern-guidelines/blob/main/FEATURES.md#L1808), interface{} cannot be used as a type constraint, whereas any is explicitly designed for this purpose.

Attempting to use interface{} as a constraint results in a compilation error:

// Illegal: interface{} cannot be used as a constraint
func Process[T interface{}](value T) { }

The correct modern pattern uses any:

// Valid: any is designed for unconstrained generics
func Process[T any](value T) { }

This distinction makes any essential when defining functions that accept any type while participating in the generic type system.

Code Migration Patterns

The guidelines in [FEATURES.md (lines 1820-1832)](https://github.com/JetBrains/go-modern-guidelines/blob/main/FEATURES.md#L1820-L1832) demonstrate the recommended migration from legacy signatures to modern idioms:

Before (Legacy):

func Decode(v interface{}) error {
    return nil
}

After (Modern):

func Decode(v any) error {
    return nil
}

For generic collections, prefer any to signal unconstrained flexibility:

// Generic function accepting any slice type
func PrintAll[T any](values []T) {
    for _, v := range values {
        fmt.Println(v)
    }
}

Reserve interface{} for scenarios requiring explicit compatibility with pre-1.18 codebases:

// Non-generic context maintaining legacy compatibility
func PrintLegacy(v interface{}) {
    fmt.Printf("%v\n", v)
}

Repository Guidelines and Tooling

The official guideline states:

"Use any instead of interface{}. any is the built-in alias for interface{} introduced with generics. Use it for unconstrained values and type parameters so the code reads in current Go terminology." — [FEATURES.md line 1810](https://github.com/JetBrains/go-modern-guidelines/blob/main/FEATURES.md#L1810)

This convention is enforced not only for human readability but also for automated tooling. The file plugin/skills/use-modern-go/SKILL.md indicates that these patterns are consumed by code generation agents, ensuring that AI-assisted development adheres to modern Go standards established in the [README.md](https://github.com/JetBrains/go-modern-guidelines/blob/main/README.md).

Summary

• any is the preferred choice for modern Go code, generic type parameters ([T any]), and conveying "unconstrained value" semantics.
• interface{} remains valid but should be restricted to legacy codebases, non-generic APIs, or when explicit backward compatibility is required.
• Compiler impact is identical; the difference is purely semantic and maintainability-focused.
• Type constraints represent the technical boundary where only any is permitted in generic contexts.

Frequently Asked Questions

Are any and interface{} interchangeable in Go?

Yes, they are fully interchangeable at the type system and runtime level because any is strictly a type alias for interface{}. You can assign values between them freely, and they compile to identical machine code. The difference lies exclusively in code readability and the ability to use any as a generic constraint.

Can I use interface{} as a generic type constraint?

No, this is explicitly prohibited by the Go compiler. As noted in the JetBrains guidelines, func Foo[T interface{}](v T) is illegal syntax. You must use any (or a specific interface) when defining unconstrained type parameters in generic functions and types.

Does switching from interface{} to any affect performance?

No, there is zero performance impact. Both identifiers resolve to the same underlying empty interface type during compilation. The change is purely cosmetic and semantic, aimed at aligning code with post-Go 1.18 idioms without altering runtime characteristics.

When should I keep using interface{} instead of migrating to any?

Maintain interface{} when working with codebases that must compile on Go versions prior to 1.18, or when integrating with legacy libraries that explicitly expect the interface{} type in their public APIs. For all new development and internal refactoring, the guidelines recommend adopting any.

{
  "mcpServers": {
    "instagit": {
      "command": "npx",
      "args": ["-y", "instagit@latest"]
    }
  }
}