Patterns: creation · 3 MIN READ

Factory Method: supply the creation step

Vary product creation without duplicating the algorithm that uses it.

Vary product creation without duplicating the algorithm that uses it. The classic Factory Method lets an algorithm ask an overridable creation operation for a product. Trace the worked Go example, then compare the benefit with the cost before applying this design to your own project.

Creational pattern · A MAP OF THE IDEA

Caller supplies a creation hook
Stable algorithm asks for a product
Algorithm uses the product contract

Useful when

An algorithm should vary product creation
Tests need a predictable product implementation

Watch out

Constructor injection may be simpler
Creation must define errors and cleanup ownership

Implementation & operation cost: Low to medium

Fit depends on the task

Small tool or CLI3/5

Domain-rich application4/5

Independent distributed services3/5

Editorial suitability, not benchmarks or a universal ranking. Styles describe different axes and can be combined.

The design decision

The classic Factory Method lets an algorithm ask an overridable creation operation for a product. Go usually replaces the inheritance hook with a function or small interface. Preserve that separation: a switch returning objects by name is a simple factory, not the full classic structure.

A complete Go example

Read this program from the entry point and follow the calls shown in the diagram. The output is included at the end so you can check the behavior without a compiler.

package main

import (
	"bytes"
	"fmt"
	"io"
)

type Report struct{ NewWriter func() io.Writer }

func (r Report) Write() io.Writer {
	w := r.NewWriter()
	fmt.Fprint(w, "report")
	return w
}

func main() {
	r := Report{NewWriter: func() io.Writer { return &bytes.Buffer{} }}
	w := r.Write()
	fmt.Println(w.(*bytes.Buffer).String())
}

// Output:
// report

Read the code

Report.Write owns the stable algorithm and calls the supplied creation hook. main chooses a buffer product without rewriting the report logic. The type assertion is used only to inspect this known test product, not as the algorithm’s dependency.

Tradeoffs and the simpler alternative

Use a plain constructor when the caller can create the dependency directly. Real writers can fail, so production report code should return write errors and define who closes the writer. A factory function should not hide expensive creation or ownership rules.

TAKE THIS WITH YOU

Varies creation through an algorithm’s supplied hook. Use a plain constructor when the caller can create the dependency directly. Real writers can fail, so production report code should return write errors and define who closes the writer. A factory function should not hide expensive creation or ownership rules.

Check your understanding

Which statement best describes Factory Method: supply the creation step?

Go to the source

Progress stays in this browser. No account needed.