populate_example_test.go

// Copyright (c) 2019 Uber Technologies, Inc.
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.

package fx_test

import (
	"context"
	"fmt"

	"go.uber.org/fx"
)

func ExamplePopulate() {
	// Some external module that provides a user name.
	type Username string
	UserModule := fx.Provide(func() Username { return "john" })

	// We want to use Fx to wire up our constructors, but don't actually want to
	// run the application - we just want to yank out the user name.
	//
	// This is common in unit tests, and is even easier with the fxtest
	// package's RequireStart and RequireStop helpers.
	var user Username
	app := fx.New(
		UserModule,
		fx.NopLogger, // silence test output
		fx.Populate(&user),
	)
	if err := app.Start(context.Background()); err != nil {
		panic(err)
	}
	defer app.Stop(context.Background())

	fmt.Println(user)

	// Output:
	// john
}