I am trying to build a multi level Validator object that is fairly generic. The idea being you have levels of validations if Level 1 passes then you do Level 2, etc. but I am struggling with one specific area: creating a function call but not executing it until a later point.
Data:
case class FooData(alpha: String, beta: String) extends AllData
case class BarData(gamma: Int, delta: Int) extends AllData
ValidationError:
case class ValidationError(code: String, message: String)
Validator:
object Validator {
def validate(validations: List[List[Validation]]): List[ValidationError] = {
validations match {
case head :: nil => // Execute the functions and get the results back
// Recursively work down the levels (below syntax may be incorrect)
case head :: tail => validate(head) ... // if no errors then validate(tail) etc.
...
}
}
}
Sample Validator:
object CorrectNameFormatValidator extends Validation {
def validate(str: String): Seq[ValidationError] = {
...
}
}
How I wish to use it:
object App {
def main(args: Array[String]): Unit = {
val fooData = FooData(alpha = "first", beta = "second")
val levelOneValidations = List(
CorrectNameFormatValidator(fooData.alpha),
CorrectNameFormatValidator(fooData.beta),
SomeOtherValidator(fooData.beta)
)
// I don't want these to execute as function calls here
val levelTwoValidations = List(
SomeLevelTwoValidator (fooData.alpha),
SomeLevelTwoValidator(fooData.beta),
SomeOtherLevelValidator(fooData.beta),
SomeOtherLevelValidator(fooData.alpha)
)
val validationLevels = List(levelOneValidations, levelTwoValidations)
Validator.validate(validationLevels)
}
}
Am I doing something really convoluted when I don't need to be or am I just missing a component?
Essentially I want to define when a function will be called and with which parameters but I don't want the call to happen until I say within the Validator. Is this something that's possible?
You can use lazy val or def when defining levelOneValidation, levelTwoValidations and validationLevel:
object App {
def main(args: Array[String]): Unit = {
val fooData = FooData(alpha = "first", beta = "second")
lazy val levelOneValidations = List(
CorrectNameFormatValidator(fooData.alpha),
CorrectNameFormatValidator(fooData.beta),
SomeOtherValidator(fooData.beta)
)
// I don't want these to execute as function calls here
lazy val levelTwoValidations = List(
SomeLevelTwoValidator (fooData.alpha),
SomeLevelTwoValidator(fooData.beta),
SomeOtherLevelValidator(fooData.beta),
SomeOtherLevelValidator(fooData.alpha)
)
lazy val validationLevels = List(levelOneValidations, levelTwoValidations)
Validator.validate(validationLevels)
}
}
You also need to change validate method to get the validations ByName and not
ByValue using : => :
object Validator {
def validate(validations: => List[List[Validation]]): List[ValidationError] = {
validations match {
case head :: nil => // Execute the functions and get the results back
// Recursively work down the levels (below syntax may be incorrect)
case head :: tail => validate(head) ... // if no errors then validate(tail) etc.
...
}
}
}
Anyway, I think you can implement it differently by just using some OOP design patterns, like Chain of Responsibility.
I'm trying to build a generic router for a personal project by Binding.scala.
I've defined a PageState trait
sealed trait WhistState {
def text: String
def hash: String
def render: Binding[Node]
}
with a number of subclasses for each route type. I've then trying to create a router, which based on the hash chooses the correct class.
object Router {
val defaultState: WhistState = DefaultState("Games")
val allStates: Vector[WhistState] = Vector(defaultState)
val route: Route.Hash[WhistState] = Route.Hash[WhistState](defaultState)(new Route.Format[WhistState] {
override def unapply(hashText: String): Option[WhistState] = allStates.find(_.hash == window.location.hash)
override def apply(state: WhistState): String = state.hash
})
route.watch()
}
And then I'm my application classes im trying to use this
object Application {
import example.route.Router._
#dom
def render: Binding[Node] = {
for (hash <- route.state.bind.hash) yield println("hash: " + hash)
route.state.bind match {
case default: WhistState => println("default"); default.render.bind
case _ => println("none"); <div>NotFound</div>
}
}
def main(args: Array[String]): Unit = {
dom.render(document.querySelector("#content"), render)
}
}
I've would expect that changing the hash would force a reevaluation of route.state.bind match ... expression.
Any idea to why this doesn't work?
Best regards
route.state is only changed when unapply returns a Some(newState) and newState does not equal to the previous state.
In your case, unapply always returns Some(defaultState) or None. That's why route.state never changes.
My use case has case classes something like
case class Address(name:String,pincode:String){
override def toString =name +"=" +pincode
}
case class Department(name:String){
override def toString =name
}
case class emp(address:Address,department:Department)
I want to create a DSL like below.Can anyone share the links about how to create a DSL and any suggestions to achieve the below.
emp.withAddress("abc","12222").withDepartment("HR")
Update:
Actual use case class may have more fields close to 20. I want to avoid redudancy of code
I created a DSL using reflection so that we don't need to add every field to it.
Disclamer: This DSL is extremely weakly typed and I did it just for fun. I don't really think this is a good approach in Scala.
scala> create an Employee where "homeAddress" is Address("a", "b") and "department" is Department("c") and that_s it
res0: Employee = Employee(a=b,null,c)
scala> create an Employee where "workAddress" is Address("w", "x") and "homeAddress" is Address("y", "z") and that_s it
res1: Employee = Employee(y=z,w=x,null)
scala> create a Customer where "address" is Address("a", "b") and "age" is 900 and that_s it
res0: Customer = Customer(a=b,900)
The last example is the equivalent of writing:
create.a(Customer).where("address").is(Address("a", "b")).and("age").is(900).and(that_s).it
A way of writing DSLs in Scala and avoid parentheses and the dot is by following this pattern:
object.method(parameter).method(parameter)...
Here is the source:
// DSL
object create {
def an(t: Employee.type) = new ModelDSL(Employee(null, null, null))
def a(t: Customer.type) = new ModelDSL(Customer(null, 0))
}
object that_s
class ModelDSL[T](model: T) {
def where(field: String): ValueDSL[ModelDSL2[T], Any] = new ValueDSL(value => {
val f = model.getClass.getDeclaredField(field)
f.setAccessible(true)
f.set(model, value)
new ModelDSL2[T](model)
})
def and(t: that_s.type) = new { def it = model }
}
class ModelDSL2[T](model: T) {
def and(field: String) = new ModelDSL(model).where(field)
def and(t: that_s.type) = new { def it = model }
}
class ValueDSL[T, V](callback: V => T) {
def is(value: V): T = callback(value)
}
// Models
case class Employee(homeAddress: Address, workAddress: Address, department: Department)
case class Customer(address: Address, age: Int)
case class Address(name: String, pincode: String) {
override def toString = name + "=" + pincode
}
case class Department(name: String) {
override def toString = name
}
I really don't think you need the builder pattern in Scala. Just give your case class reasonable defaults and use the copy method.
i.e.:
employee.copy(address = Address("abc","12222"),
department = Department("HR"))
You could also use an immutable builder:
case class EmployeeBuilder(address:Address = Address("", ""),department:Department = Department("")) {
def build = emp(address, department)
def withAddress(address: Address) = copy(address = address)
def withDepartment(department: Department) = copy(department = department)
}
object EmployeeBuilder {
def withAddress(address: Address) = EmployeeBuilder().copy(address = address)
def withDepartment(department: Department) = EmployeeBuilder().copy(department = department)
}
You could do
object emp {
def builder = new Builder(None, None)
case class Builder(address: Option[Address], department: Option[Department]) {
def withDepartment(name:String) = {
val dept = Department(name)
this.copy(department = Some(dept))
}
def withAddress(name:String, pincode:String) = {
val addr = Address(name, pincode)
this.copy(address = Some(addr))
}
def build = (address, department) match {
case (Some(a), Some(d)) => new emp(a, d)
case (None, _) => throw new IllegalStateException("Address not provided")
case _ => throw new IllegalStateException("Department not provided")
}
}
}
and use it as emp.builder.withAddress("abc","12222").withDepartment("HR").build().
You don't need optional fields, copy, or the builder pattern (exactly), if you are willing to have the build always take the arguments in a particular order:
case class emp(address:Address,department:Department, id: Long)
object emp {
def withAddress(name: String, pincode: String): WithDepartment =
new WithDepartment(Address(name, pincode))
final class WithDepartment(private val address: Address)
extends AnyVal {
def withDepartment(name: String): WithId =
new WithId(address, Department(name))
}
final class WithId(address: Address, department: Department) {
def withId(id: Long): emp = emp(address, department, id)
}
}
emp.withAddress("abc","12222").withDepartment("HR").withId(1)
The idea here is that each emp parameter gets its own class which provides a method to get you to the next class, until the final one gives you an emp object. It's like currying but at the type level. As you can see I've added an extra parameter just as an example of how to extend the pattern past the first two parameters.
The nice thing about this approach is that, even if you're part-way through the build, the type you have so far will guide you to the next step. So if you have a WithDepartment so far, you know that the next argument you need to supply is a department name.
If you want to avoid modifying the origin classes you can use implicit class, e.g.
implicit class EmpExtensions(emp: emp) {
def withAddress(name: String, pincode: String) {
//code omitted
}
// code omitted
}
then import EmpExtensions wherever you need these methods
Need to extract tokens and fixed text. Example:
"Hello {token1} today's date is {token2} would you like to call {token3}"
would return
FixedPart("Hello ")
TokenPart(token1)
FixedPart(" today's date is ")
TokenPart(token2)
FixedPart(" would you like to call ")
TokenPart(token3)
Here is naive implementation
import org.parboiled2.ParserInput
import org.parboiled2.Parser
import org.parboiled2.CharPredicate
sealed trait Part
case class TokenPart(tokenName : String ) extends Part
case class FixedPart( text : String ) extends Part
class MyParser(val input: ParserInput) extends Parser {
def Token = rule { '{' ~ capture(TokenName) ~> (TokenPart(_)) ~'}' }
//how this should be implemented??
def NotToken = rule { capture (!Token) ~>(FixedPart(_) )}
def TokenName = rule { CharPredicate.Alpha ~ oneOrMore (CharPredicate.AlphaNum) }
// This would not work
def TokenNotToken = rule { (Token|NotToken) }
def InputLine = rule { zeroOrMore (TokenNotToken) }
}
object MyParser {
def main(args: Array[String]) {
val res = new MyParser("Hello {token1} today's date is {token2} would you like to call {token3}").InputLine.run() // Success
println( res )
}
}
Any other to implement this ??
Hi I modified your code and added some comments (I hope they will be helpful), so it works, and (I guess) does what you wanted it to do:
import org.parboiled2.ParserInput
import org.parboiled2.Parser
import org.parboiled2.CharPredicate
sealed trait Token
case class TokenPart(tokenName : String) extends Token
case class StringToken(text: String) extends Token
// I moved pre-evaluated char predicates to the companion
// you may leave them inside the class if you want.
// I also moved literals like startToken and endToken here
object TokenExtractor {
val AlphaChar = CharPredicate.Alpha
val AlphaNum = CharPredicate.AlphaNum
val startToken = "{"
val endToken = "}"
}
class TokenExtractor(val input: ParserInput) extends Parser {
import TokenExtractor._
// may be you wanted zero or more? Anyway in this case
// shortcut can play nice here. In fact, if you want to stick
// with oneOrMore you can user AlphaNum.+ instead
def TokenName = rule {
AlphaChar ~ AlphaNum.*
}
// There's a shortcut for Extraction syntax. If you are extracting
// data to the case class and Rule arguments match the number of
// items in the case class's apply method
// you can simply give a name of this case class:
// the extraction operator '~>' should be located at the end of the
// from the official documtation:
// https://github.com/sirthias/parboiled2
// One more very useful feature is special support for
// case class instance creation:
//
// case class Person(name: String, age: Int)
// (foo: Rule2[String, Int]) ~> Person
//
def Token = rule {
startToken ~ capture(TokenName) ~ endToken ~> TokenPart
}
// the text should follow until the parser will meet the
// enclosing '{' character. Disclosing is not mandatory :)
def Text = rule {
oneOrMore(noneOf(startToken))
}
// Here we're capturing a data that matches
// pre-defined rule (in our case Text)
def TextString = rule {
capture(Text) ~> StringToken
}
def TextPart = rule {
TextString | Token
}
// EOI is mandatory. Parser is greedy, so it tells the parser
// where parsing procedure must end, so please, add it at the
// end of the input
def InputLine = rule {
zeroOrMore(TextPart) ~ EOI
}
}
object Main {
def main(args: Array[String]) {
val example =
"Hello {token1} today's date is {token2} would you like to call {token3}"
// parser input can be string, so put it inside the constructor
val result = new TokenExtractor(example).InputLine.run()
println(result)
}
}
In a play 2.1 application I have the following code (it's just a request wrapper that gets rid of any trailing slash):
class NormalizedRequest(request: RequestHeader) extends RequestHeader {
val headers = request.headers
val id = request.id
val method = request.method
val queryString = request.queryString
val remoteAddress = request.remoteAddress
val tags = request.tags
val version = request.version
// strip first part of path and uri if it matches http.path config
val path = if (request.path == "/") "/" else request.path.stripSuffix("/")
val uri = path + {
if(request.rawQueryString == "") ""
else "?" + request.rawQueryString
}
}
object NormalizedRequest {
def apply(request: RequestHeader) = new NormalizedRequest(request)
}
This kind of code is pretty common, you just wrap an object inside another
I was wondering if there's an easier way to acomplish it, ideally it would be something like (pseudo code inspired on case classes):
object NormalizedRequest {
def apply(request: RequestHeader) = {
val path = if (request.path == "/") "/" else request.path.stripSuffix("/")
val uri = path + {
if(request.rawQueryString == "") ""
else "?" + request.rawQueryString
}
request.copy(path = path, uri = uri)
}
}
If I understand correctly, you're asking for a more concise version of the Decorator pattern in scala. You still need your "wrapper" to be the same type as you inner class (by extending it or a common base/trait) in order to be able to pass it over to some function that expects to receive an instance of the inner class (or of the common base/trait).
What you wrote in your pseudo code is actually almost legal scala, you just have to change the definition of apply in NormalizedRequest to return an anonymous class that extends RequestHeader.
I.e. instead of
class NormalizedRequest(request: RequestHeader) extends RequestHeader {
//.... "decorated" logic here
}
object NormalizedRequest {
def apply(request: RequestHeader) = new NormalizedRequest(request)
}
you would have
object NormalizedRequest {
def apply(request: RequestHeader) = new RequestHeader {
// ...
// instead of having a separate NormalizedRequest class
// define its behaviour here in anonymous form
}
}
A simplified example:
// our inner class and companion object
// (a simplified version of your RequestHeader)
class Inner() {def test="hello"}; object Inner {
def apply() = new Inner()
}
// our wrapper
object Outer {
def apply(inner: Inner) = new Inner {
override def test=inner.test + "!"
}
}
however, although it saves you a few keystrokes, I really think you would lose in readability.