如何为play2的表单定义StopOnFirstFail dsl? [英] How to define a StopOnFirstFail dsl for play2's form?
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问题描述
In this question: If a form field has multi validators, how to let play verify them one by one, not all?, Julien gave me a method named stopOnFirstFail
to solve my problem:
def stopOnFirstFail[T](constraints: Constraint[T]*) = Constraint { field: T =>
constraints.toList dropWhile (_(field) == Valid) match {
case Nil => Valid
case constraint :: _ => constraint(field)
}
}
它的用法是:
val loginForm = Form(
"name" -> (text verifying stopOnFirstFail( nonEmpty, minLength(4) ))
)
但是我希望定义一个dsl,它可以用作:
But I hope to define a dsl which can be used as:
val loginForm = Form(
"name" -> (text verifying ( nonEmpty or minLength(4) ))
)
我试图为play.api.data.validation.Constraint
定义一个隐式方法:
I tried to defined an implicit method for play.api.data.validation.Constraint
:
import play.api.data.validation._
implicit def _Constraint[T](cons: Constraint[T]) = new {
def or[T](other: Constraint[T]) = Constraint { field: T =>
cons(field) match { // (!)
case Valid => other(field)
case invalid => invlaid
}
}
}
但是它无法编译,(!)行中的错误是,消息是:
But it can't be compiled, the error in on the (!) line, and message is:
type mismatch;
found: field.type (with underlying type T) required: T
Note: implicit method _Constraint is not applicable here
because it comes after the application point and it lacks an explicit result type
如何解决?
推荐答案
or
方法不使用类型参数:
The or
method does not take a type parameter:
implicit def toLazyOr[T](cons: Constraint[T]) = new {
def or(other: Constraint[T]) = Constraint { field: T =>
cons(field) match {
case Valid => other(field)
case Invalid => Invalid
}
}
}
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