docs/_docs/reference/error-codes/E153.md
This error occurs when summonFrom is used with an invalid pattern in a case clause. The summonFrom macro only accepts typed patterns (x: T) or wildcard patterns (_).
summonFrom is a compile-time construct that tries to summon an implicit value. It requires patterns that check for the presence of an implicit, not arbitrary value patterns.
import scala.compiletime.summonFrom
inline def example = summonFrom {
case 42 => "found"
}
-- [E153] Syntax Error: example.scala:4:7 --------------------------------------
4 | case 42 => "found"
| ^^
| Unexpected pattern for summonFrom. Expected `x: T` or `_`
|-----------------------------------------------------------------------------
| Explanation (enabled by `-explain`)
|- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
| The pattern "42" provided in the case expression of the summonFrom,
| needs to be of the form `x: T` or `_`.
|
| Example usage:
| inline def a = summonFrom {
| case x: T => ???
| }
|
| or
| inline def a = summonFrom {
| case _ => ???
| }
-----------------------------------------------------------------------------
import scala.compiletime.summonFrom
// Use typed pattern to check for implicit presence
inline def example = summonFrom {
case given String => "found a String"
case _ => "not found"
}
import scala.compiletime.summonFrom
// Use binding with type pattern
inline def example2 = summonFrom {
case s: String => s"found: $s"
case _ => "not found"
}