RaycastHit2D implements the C# implicit bool operator. This allows it to be used in an if statement to check whether a hit is found.
public static implicit operator bool(RaycastHit2D hit) => (Object) hit.collider != (Object) null;
Example
RaycastHit2D hit = Physics2D.Raycast(someStartPoint, someDirection);
if(hit) {
Debug.Log("yaaay I hit something!");
}
This is also valid:
RaycastHit2D hit = Physics2D.Raycast(someStartPoint, someDirection);
bool rayHitSomthing = hit;