You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: extract.go
    path of file: ./repos/sealer/vendor/go.uber.org/fx
    
    the code of the file until where you have to start completion: // 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

import (
	"fmt"
	"reflect"
	"unicode"
	"unicode/utf8"
)

var _typeOfIn = reflect.TypeOf(In{})

// Extract fills the given struct with values from the dependency injection
// container on application initialization. The target MUST be a pointer to a
// struct. Only exported fields will be filled.
//
// Extract will be deprecated soon: use Populate instead, which doesn't
// require defining a container struct.
func Extract(tar
    
func Extract(target interface{}) Option {
	v := reflect.ValueOf(target)

	if t := v.Type(); t.Kind() != reflect.Ptr || t.Elem().Kind() != reflect.Struct {
		return Error(fmt.Errorf("Extract expected a pointer to a struct, got a %v", t))
	}

	v = v.Elem()
	t := v.Type()

	// We generate a function which accepts a single fx.In struct as an
	// argument. This struct contains all exported fields of the target
	// struct.

	// Fields of the generated fx.In struct.
	fields := make([]reflect.StructField, 0, t.NumField()+1)

	// Anonymous dig.In field.
	fields = append(fields, reflect.StructField{
		Name:      _typeOfIn.Name(),
		Anonymous: true,
		Type:      _typeOfIn,
	})

	// List of values in the target struct aligned with the fields of the
	// generated struct.
	//
	// So for example, if the target is,
	//
	// 	var target struct {
	// 		Foo io.Reader
	// 		bar []byte
	// 		Baz io.Writer
	// 	}
	//
	// The generated struct has the shape,
	//
	// 	struct {
	// 		fx.In
	//
	// 		F0 io.Reader
	// 		F2 io.Writer
	// 	}
	//
	// And `targets` is,
	//
	// 	[
	// 		target.Field(0),  // Foo io.Reader
	// 		target.Field(2),  // Baz io.Writer
	// 	]
	//
	// As we iterate through the fields of the generated struct, we can copy
	// the value into the corresponding value in the targets list.
	targets := make([]reflect.Value, 0, t.NumField())

	for i := 0; i < t.NumField(); i++ {
		f := t.Field(i)

		// Skip unexported fields.
		if f.Anonymous {
			// If embedded, StructField.PkgPath is not a reliable indicator of
			// whether the field is exported. See
			// https://github.com/golang/go/issues/21122

			t := f.Type
			if t.Kind() == reflect.Ptr {
				t = t.Elem()
			}

			if !isExported(t.Name()) {
				continue
			}
		} else if f.PkgPath != "" {
			continue
		}

		// We don't copy over names or embedded semantics.
		fields = append(fields, reflect.StructField{
			Name: fmt.Sprintf("F%d", i),
			Type: f.Type,
			Tag:  f.Tag,
		})
		targets = append(targets, v.Field(i))
	}

	// Equivalent to,
	//
	// 	func(r struct {
	// 		fx.In
	//
	// 		F1 Foo
	// 		F2 Bar
	// 	}) {
	// 		target.Foo = r.F1
	// 		target.Bar = r.F2
	// 	}

	fn := reflect.MakeFunc(
		reflect.FuncOf(
			[]reflect.Type{reflect.StructOf(fields)},
			nil,   /* results */
			false, /* variadic */
		),
		func(args []reflect.Value) []reflect.Value {
			result := args[0]
			for i := 1; i < result.NumField(); i++ {
				targets[i-1].Set(result.Field(i))
			}
			return nil
		},
	)

	return Invoke(fn.Interface())
}