Template Method

The Problem

Several workflows may share the same broad algorithm but differ in a few steps. Batch jobs, import pipelines, and sync tasks often repeat the same fetch-transform-persist structure. Duplicating the whole algorithm just to vary one stage makes the shared flow harder to maintain.

The Solution

Template Method fixes the high-level sequence while allowing specific steps to vary. In Go, this is often expressed without inheritance by using a runner function plus a small interface of hooks. The overall algorithm stays in one place, and concrete jobs provide only the variable steps.

Structure

flowchart TD
Client["Client"]
Runner["RunSync
template runner"]
Hooks["SyncHooks
interface"]
InventoryJob["InventorySyncJob"]
CatalogJob["CatalogSyncJob"]

Client -->|"RunSync(job)"| Runner
Runner -->|"FetchRecords()"| Hooks
Runner -->|"Transform()"| Hooks
Runner -->|"Persist()"| Hooks
InventoryJob -.->|"implements"| Hooks
CatalogJob -.->|"implements"| Hooks

• Template runner: RunSync defines the fixed algorithm sequence.
• Hook interface: SyncHooks declares the steps that can vary.
• Concrete jobs: Inventory and catalog sync jobs provide different fetch and transform logic.
• Client: Passes a concrete job into the runner.

Implementation

This example runs a sync pipeline with a shared algorithm: fetch records, transform them, and persist the output. Different jobs customize the step behavior without rewriting the pipeline skeleton.

package main

import "fmt"

type SyncHooks interface {
	Name() string
	Fetch() []string
	Transform(records []string) []string
	Persist(records []string) error
}

func RunSync(job SyncHooks) error {
	fmt.Println("running", job.Name())
	records := job.Fetch()
	transformed := job.Transform(records)
	return job.Persist(transformed)
}

package main

import (
	"fmt"
	"strings"
)

type InventorySync struct{}

type CatalogSync struct{}

func (InventorySync) Name() string { return "inventory-sync" }
func (CatalogSync) Name() string   { return "catalog-sync" }

func (InventorySync) Fetch() []string {
	return []string{"kb-001", "mon-002"}
}

func (CatalogSync) Fetch() []string {
	return []string{"keyboard", "monitor"}
}

func (InventorySync) Transform(records []string) []string {
	out := make([]string, 0, len(records))
	for _, record := range records {
		out = append(out, strings.ToUpper(record))
	}
	return out
}

func (CatalogSync) Transform(records []string) []string {
	out := make([]string, 0, len(records))
	for _, record := range records {
		out = append(out, titleCase(record))
	}
	return out
}

// titleCase capitalizes the first letter of each space-separated word.
// strings.Title is deprecated; product names here are plain ASCII, so a
// small local helper avoids pulling in golang.org/x/text for a demo.
func titleCase(s string) string {
	words := strings.Fields(s)
	for i, word := range words {
		words[i] = strings.ToUpper(word[:1]) + word[1:]
	}
	return strings.Join(words, " ")
}

func (InventorySync) Persist(records []string) error {
	fmt.Println("persist inventory", records)
	return nil
}

func (CatalogSync) Persist(records []string) error {
	fmt.Println("persist catalog", records)
	return nil
}

package main

import "fmt"

func main() {
	fmt.Println("=== Template Method in Go ===")

	_ = RunSync(InventorySync{})
	_ = RunSync(CatalogSync{})
}

Real-World Analogy

Think of a baking recipe. The overall sequence stays fixed: prepare, mix, bake, cool. Different recipes vary the ingredients or timings of specific steps, but they still follow the same skeleton.

Pros and Cons

| Pros | Cons | | --- | --- | | Keeps the shared workflow in one place. | The fixed skeleton can become too rigid as workflows diverge. | | Reduces duplication across similar pipelines. | Hook contracts can become awkward if too many steps vary. | | Lets implementations customize only the steps that vary. | Less flexible than Strategy when the whole algorithm should change. |

Best Practices

• Keep the fixed algorithm in one place so shared workflow changes happen once.
• Use a small hook interface that reflects only the steps that vary.
• In Go, prefer composition and function-driven hooks over inheritance-heavy designs.
• Reserve Template Method for workflows with a real stable skeleton, not just loosely similar functions.
• If the algorithm itself should vary, Strategy is usually a better fit.

When to Use

• Several workflows share the same ordered pipeline but differ in a few steps.
• You want the common sequence enforced consistently.
• Concrete jobs should customize behavior without duplicating the full algorithm.

When NOT to Use

• The steps do not actually follow one stable skeleton.
• Each workflow varies so much that a shared template becomes brittle.
• A plain helper function or Strategy would express the reuse more simply.