go-functional-options

Implement Go functional options with With* constructors and an Option interface.

Updated Feb 28, 2026

Search Tags:#golang #go #constructor #functional-options #design-pattern #api-construction

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npx skills add https://github.com/rondevz/phant --skill go-functional-options-rondevz

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Please help me install this Agent Skill.
Skill: go-functional-options
Source: https://github.com/rondevz/phant/tree/main/.agents/skills/go-functional-options
Command: npx skills add https://github.com/rondevz/phant --skill go-functional-options-rondevz

SYSTEM DOCUMENTATION & REQUIREMENTS

What problem does it solve?

Go constructors often require many optional parameters, leading to brittle and hard-to-read call sites. Functional options pattern solves this by using an opaque options struct, an exported Option interface, and With* constructors to apply configuration while keeping sensible defaults.

Core Features & Use Cases

Extensible API design with With* options
Centralized defaults management
Clear, readable caller experience

Quick Start

Create a minimal Go example that defines an unexported options struct, an exported Option interface with apply, With* option constructors, and a constructor that applies options to defaults.

Frequently Asked Questions about go-functional-options

High-intent search queries and answers about installing and using this skill.

FAQPage Schema

How do I handle multiple optional parameters in a Go constructor?▼

The functional options pattern solves Go API configuration complexity by using an unexported options struct and exported With* constructors. Callers only configure what differs from the defaults, keeping call sites readable and extensible.

What is the functional options pattern in Golang?▼

The functional options pattern in Golang uses an exported Option interface with an apply method and With* constructors to configure an unexported options struct. This allows callers to override specific defaults without passing multiple parameters to a constructor.

How do I create extensible Go APIs with default configuration?▼

You create extensible Go APIs by defining an unexported options struct for defaults, an exported Option interface, and With* constructors. A base constructor then applies these functional options to the defaults, allowing callers to configure only what they need.

How do functional options improve Golang library design?▼

Functional options improve Golang library design by centralizing default management and avoiding brittle constructors with many parameters. They provide a clear, readable caller experience where developers only specify the configurations that differ from the defaults.

Does the functional options pattern require external dependencies in Go?▼

No, the functional options pattern does not require external dependencies in Go. It is implemented purely with standard language features: an unexported options struct, an exported Option interface with an apply method, and With* option constructors.

When should I not use functional options for API construction?▼

You should avoid functional options for API construction when a Go struct requires no optional parameters or has strictly mandatory fields. The pattern is designed specifically for scenarios with multiple optional configurations where defaults should be preserved.