[2.0] Type mismatch when rendering template inside pattern matching

[juhe]

  def edit(id: Long) = Action {

    transaction {

      Citizen.findById(id) match {

        case None => NotFound("Citizen not found.")

        case Some(c) => Ok(views.html.edit(c))

      }

    }

  }

with a code like this for some reason I get:
type mismatch; found : play.api.mvc.SimpleResult[_ >: java.lang.String with play.api.templates.Html <: java.io.Serializable] required: play.api.mvc.SimpleResult[_1(in method edit)] where type _1(in method edit) >: java.lang.String with play.api.templates.Html <: java.io.Serializable Note: java.io.Serializable >: _1, but class SimpleResult is invariant in type A. You may wish to define A as -A instead. (SLS 4.5) 

Why is this? If I use the same Ok return outside matching it works fine.

[Guillaume Bort]

Hum, try the return explicitly:

def edit(id: Long): Result

It is a type inference problem, I will check why.

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[juhe]

I`m still fairly new to Scala, but if you meant this:

  def edit(id: Long): Result = Action {

    transaction {

      Citizen.findById(id) match {

        case None => NotFound("Citizen not found.")

        case Some(c) => Ok(views.html.edit(c))

      }

    }

  }

It gives:

type mismatch; found : play.api.mvc.Action[play.api.mvc.AnyContent] required: play.api.mvc.Result 

On Tuesday, July 3, 2012 7:35:30 PM UTC+3, Guillaume Bort wrote:

Hum, try the return explicitly:

def edit(id: Long): Result

It is a type inference problem, I will check why.

On Tue, Jul 3, 2012 at 6:18 PM, juhe <mirko...@gmail.com> wrote:
>   def edit(id: Long) = Action {
>     transaction {
>       Citizen.findById(id) match {
>         case None => NotFound("Citizen not found.")
>         case Some(c) => Ok(views.html.edit(c))
>       }
>     }
>   }
>
> with a code like this for some reason I get:
> type mismatch; found : play.api.mvc.SimpleResult[_ >: java.lang.String with
> play.api.templates.Html <: java.io.Serializable] required:
> play.api.mvc.SimpleResult[_1(in method edit)] where type _1(in method edit)
>>: java.lang.String with play.api.templates.Html <: java.io.Serializable
> Note: java.io.Serializable >: _1, but class SimpleResult is invariant in
> type A. You may wish to define A as -A instead. (SLS 4.5)
>
> Why is this? If I use the same Ok return outside matching it works fine.
>
>
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[Guillaume Bort]

Yes sorry. You need to give explicit type to the Result. So:

Citizen.findById(id) match {
case None => NotFound("Citizen not found.")
case Some(c) => Ok(views.html.edit(c))

}:Result

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>>
>>
>> --
>> Guillaume Bort, http://guillaume.bort.fr
>

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[juhe]

This is not syntactically correct :) Can you even force pattern match into specific type? Anyways hope this issue gets fixed, cause pattern matching enables some really neat and concise actions.

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[Nilanjan]

What about this?

transaction {
val r: Result = Citizen.findById(id) match {

    case None => NotFound("Citizen not found.")
    case Some(c) => Ok(views.html.edit(c))
}

r
}


Nilanjan

[juhe]

  def edit(id: Long) = Action {

    transaction {

      val r:Result = Citizen.findById(id) match {

        case None => NotFound("Citizen not found.")

        case Some(c) => Ok(views.html.edit(c))

      }

      r

    }

  }

This does work, but now its boilerplate all over and kind of defeats the purpose. Guillaume let me know if I can provide any more data to help fix this issue, tho its relatively simple to reproduce.

[juhe]

Any updates on this?

[Guillaume Bort]

I'm not sure why the type inference doesn't work properly here and if
we could change something to make it work, but you can also specify
the type to solve this issue:

def edit(id: Long) = Action {

inTransaction {
Citizen.findById(id).map { c =>
Ok(views.html.edit(c))
}.getOrElse(NotFound("Citizen not found."))
}:Result
}

On Mon, Jul 30, 2012 at 7:29 AM, Thomas Rawyler <raw...@gmail.com> wrote:
> I'd like to add that the small boilerplate addition works as well with the
> getOrElse variant.

>
> def edit(id: Long) = Action {

> inTransaction {
> val r = Citizen.findById(id).map { c =>
> Ok(views.html.edit(c))
> }.getOrElse(NotFound("Citizen not found."))
> r
> }
> }
>
> but of course would look more beautiful like this if it would compile:

>
> def edit(id: Long) = Action {

> inTransaction {
> Citizen.findById(id).map { c =>
> Ok(views.html.edit(c))
> }.getOrElse(NotFound("Citizen not found."))
> }
> }
>
> (btw, I prefer to use inTransaction (propagation required) instead of
> transaction (require new))

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>>>>>> >>
>>>>>> >>
>>>>>> >> --
>>>>>> >> Guillaume Bort, http://guillaume.bort.fr
>>>>>> >
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>>>>>>
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>>>>>>
>>>>>> --
>>>>>> Guillaume Bort, http://guillaume.bort.fr
>
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[Thomas Rawyler]

I tried the type hint suggestion before but still got the same type inference compilation error.

To make it work I hat to put the type after the getOrElse clause:

def edit(id: Long) = Action { 
    inTransaction { 
      Citizen.findById(id).map { c => 
        Ok(views.html.edit(c)) 
      }.getOrElse(NotFound("Citizen not found.")): Result
    }
}

Thanks again for the suggestion. It's a workaround but at least it's small.

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>>>>>> >>
>>>>>> >> --
>>>>>> >> Guillaume Bort, http://guillaume.bort.fr
>>>>>> >
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>>>>>> --
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