IsType

Nominal type predicate. IsType[A] is satisfied only when the Scala type being checked is exactly A (i.e. checked =:= A).

This is the building block for precise element-type constraints. The canonical use-case is constraining the element type of a polymorphic DSL method so that no separate type-alignment proof (e.g. a Containable type class) is needed:

import zio.blocks.schema.comptime.Allows
import Allows._
import zio.blocks.typeid.IsNominalType

trait ConditionExpression[From]

trait Column[From, To] {
 // `To` must be a Set whose element type is exactly `A`.
 // `IsNominalType[A]` ensures A is concrete at the call site.
 def contains[A: IsNominalType](a: A)(implicit
   ev: Allows[To, Sequence.Set[IsType[A]]]
 ): ConditionExpression[From]
}

IsType[A] can also replace specific primitive nodes as type aliases:

import zio.blocks.schema.comptime.Allows._

type MyInt = IsType[scala.Int]  // equivalent to Primitive.Int semantically

Requires that A is a concrete nominal type. Combining with IsNominalType[A] (from zio-blocks-typeid) at the call site ensures the macro always sees a concrete A.