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: context.go
    path of file: ./repos/podman/vendor/github.com/go-openapi/validate
    
    the code of the file until where you have to start completion: package validate

import (
	"context"
)

// validateCtxKey is the key type of context key in this pkg
type validateCtxKey string

const (
	operationTypeKey validateCtxKey = "operationTypeKey"
)

type operationType string

const (
	request  operationType = "request"
	response operationType = 
    
func extractOperationType(ctx context.Context) operationType {
	v := ctx.Value(operationTypeKey)
	if v == nil {
		return none
	}
	res, ok := v.(operationType)
	if !ok {
		return none
	}
	// validate the value is in operation enum
	if err := Enum("", "", res, operationTypeEnum); err != nil {
		return none
	}
	return res
}