unable to create an implicit read for JSON - scala

Question

My server code will receive the following JSON
{
"signin-info":{
"email" : "someemail",
"password": "password"
}
}
I have created the following 2 case classes to represent this structure.
case class UserSigninInfo(
email:String,
password:String
)
case class UserSignin(
signinInfo: UserSigninInfo
)
To read the JSON, I have created the following 2 Reads
implicit val userSigninInfoReads:Reads[UserSigninInfo] = (
(JsPath \ "email").read[String] and
(JsPath \ "password").read[String]
)(UserSigninInfo.apply _)
implicit val userSigninReads:Reads[UserSignin] = (
(JsPath \ "signin-info").read[UserSigninInfo]
)(UserSignin.apply _)
But for userSigninReads, I am getting the following compilation error. What am I doing wrong?
overloaded method value read with alternatives:
[error] (t: models.UserSigninInfo)play.api.libs.json.Reads[models.UserSigninInfo] <and>
[error] (implicit r: play.api.libs.json.Reads[models.UserSigninInfo])play.api.libs.json.Reads[models.UserSigninInfo]
[error] cannot be applied to (models.UserSigninInfo => models.UserSignin)
[error] (JsPath \ "signin-info").read[UserSigninInfo]
[error] `

Answer 1

The solution to construct reads for your main object is:
implicit val userSigninReads : Reads[UserSignin] =
(JsPath \ "signin-info").read[UserSigninInfo].map(UserSignin(_))
This is because it only has a single field.
Your construction was essentailly:
((JsPath \ "signin-info").read[UserSigninInfo])(UserSignin.apply _)
which is simply
(JsPath \ "signin-info").read[UserSigninInfo](UserSignin.apply _)
because it just adds extra ().
read method indeed has two alternatives:
def read[T](t: T) = Reads.pure(t)
def read[T](implicit r: Reads[T]): Reads[T] = Reads.at[T](this)(r)
It expects either implicit reads or explicit value, but you are passing a function, this is why compiler complains.
When you combine multiple fields with and, different object is created, e.g. FunctionalBuilder[M]#CanBuild2[A, B] for 2 elements, and it has apply method to construct final Reads instance.
As you only have one object you can create your Reads by reading UserSigninInfo from the path you want and putting the result into UserSignin with map.