docs/_docs/reference/error-codes/E140.md
This error occurs when a type alias or type definition references itself, either directly or through a chain of other type aliases, creating a cycle.
Type aliases must eventually resolve to a concrete type. When a type refers back to itself without eventually resolving to a non-circular definition, the compiler cannot determine what the type actually represents.
Use the -explain-cyclic flag to get a detailed trace of how the cyclic reference was discovered.
type A = B
type B = A
-- [E140] Cyclic Error: example.scala:1:5 --------------------------------------
1 |type A = B
| ^
|illegal cyclic type reference: alias B of type A refers back to the type itself
|
|The error occurred while trying to compute the signature of type A
| which required to explore type B for cyclic references
| which required to explore type A for cyclic references
|
| Run with both -explain-cyclic and -Ydebug-cyclic to see full stack trace.
// Break the cycle by using a concrete type
type A = Int
type B = A
// Alternative: If recursion is needed, use a class or trait
trait A:
def next: A