Combining constraints with intersection type

[mcallisto]

Is there a plain way to combine constraints?

I tried with intersection type
type +>[A, B] = A ==> Greater[B] & Even[A]

but when testing I get

Found:    (2 : Int)
Required: Int +> (0 : Int)

Even if import iron.constraint.refineValue is available.

[Iltotore]

Hello,
the use of intersection here is impossible in its current state because intersection is commutative leading to an implicit ambiguity error (multiple possibilities).

Instead, you can use the &&[A, B] alias of And:

type +>[A, B] = A ==> Greater[A] && Even[B]

EDIT: Marked as answer. Check the below comments.

[Iltotore]

It's not the same "parameter" on my last message I mean "implicit parameters". Not generic types used as parameters

[mcallisto]

This custom constraint added to my repo works for me, failing at compile time as well

package io.github.iltotore.iron.numeric

import io.github.iltotore.iron.==>
import io.github.iltotore.iron.constraint.Constraint

import scala.compiletime.{constValue, summonInline}

object constraintCustom {

  /**
   * Constraint: checks if the input value is even and greater than V.
   * @tparam V
   */
  trait EvenAndGreater[V]

  type +>[A, B] = A ==> EvenAndGreater[B]

  class EvenAndGreaterConstraint[A <: Number, V <: A] extends Constraint[A, EvenAndGreater[V]] {
    override inline def assert(value: A): Boolean = NumberOrdering.gt(value, constValue[V]) && modulo(value, 2) == 0

    override inline def getMessage(value: A): String = "value should be even and greater than the specified value"
  }

  inline given[A <: Number, V <: A]: EvenAndGreaterConstraint[A, V] = new EvenAndGreaterConstraint
  
}

[Iltotore]

That's actually normal 😋

Your constraint doesn't require implicit parameters. As you can see in the And implementation:

  class AndConstraint[A, B, C, CB <: Constraint[A, B], CC <: Constraint[A, C]](using left: CB, right: CC) extends Constraint.RuntimeOnly[A, And[B, C]] {

    override inline def assert(value: A): Boolean = left.assert(value) && right.assert(value)

    override inline def getMessage(value: A): String = s"${left.getMessage(value)} and ${right.getMessage(value)}"
  }

left and right can't be inline due to a compiler limitation leading to deferrence (at least in 3.0.0).

[mcallisto]

I guessed it was normal, but in this way I achieved what I needed 😅 , that is a combined constraint failing at compile time! Thank you for all your help!

[Iltotore]

You're welcome 😄