docs/_docs/reference/error-codes/E035.md
This error is emitted when the wildcard type syntax (_ or ?) is used in a position where it cannot be bound to a concrete type.
Replace the wildcard with a non-wildcard type. If the type doesn't matter, try replacing the wildcard with Any.
This typically happens in:
def foo(x: _) = ...val foo = List[?](1, 2)def foo[T <: _](x: T) = ...val foo: _ = 3def example(x: ?) = x
-- [E035] Syntax Error: example.scala:1:15 -------------------------------------
1 |def example(x: ?) = x
| ^
| Unbound wildcard type
|-----------------------------------------------------------------------------
| Explanation (enabled by `-explain`)
|- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
| The wildcard type syntax (_) was used where it could not be bound.
| Replace _ with a non-wildcard type. If the type doesn't matter,
| try replacing _ with Any.
|
| Examples:
|
| - Parameter lists
|
| Instead of:
| def foo(x: _) = ...
|
| Use Any if the type doesn't matter:
| def foo(x: Any) = ...
|
| - Type arguments
|
| Instead of:
| val foo = List[?](1, 2)
|
| Use:
| val foo = List[Int](1, 2)
|
| - Type bounds
|
| Instead of:
| def foo[T <: _](x: T) = ...
|
| Remove the bounds if the type doesn't matter:
| def foo[T](x: T) = ...
|
| - val and def types
|
| Instead of:
| val foo: _ = 3
|
| Use:
| val foo: Int = 3
-----------------------------------------------------------------------------
// Use Any if the type doesn't matter
def example(x: Any) = x
// Use a type parameter for generic behavior
def example[T](x: T): T = x
// Specify a concrete type
def example(x: Int) = x