E218: Illegal Erased Definition

This error is emitted when the erased modifier is used with a definition that doesn't support it.

Only non-lazy immutable values (val) can be marked as erased. The erased modifier is not allowed for:

Methods (except macros)
Lazy values (lazy val)
Mutable values (var)
Type definitions
Objects

Additionally, this error can occur when a value's type implicitly makes it erased (by extending compiletime.Erased) but the definition kind doesn't support erasure.

Example

scala

import scala.language.experimental.erasedDefinitions

object Test:
  erased lazy val x: Int = 42

Error

scala

-- [E218] Type Error: example.scala:4:18 ---------------------------------------
4 |  erased lazy val x: Int = 42
  |                  ^
  |                  `erased` is not allowed for this kind of definition.
  |-----------------------------------------------------------------------------
  | Explanation (enabled by `-explain`)
  |- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
  | Only non-lazy immutable values can be `erased`
   -----------------------------------------------------------------------------

Solution

Use erased only with non-lazy val definitions:

scala

import scala.language.experimental.erasedDefinitions

object Test:
  erased val x: Int = 42

If you need a method with erased parameters, use erased parameters instead:

scala

import scala.language.experimental.erasedDefinitions

def compute(erased hint: Int): Int = 42

<aside class="warning"> This reference page was created with LLM assistance - the description of the error code may not be accurate or cover all possible scenarios. </aside>