manual: CI check with nitunit

[nit.git] / lib / ai / backtrack.nit

diff --git a/lib/ai/backtrack.nit b/lib/ai/backtrack.nit
index ddc68ef..597164d 100644 (file)
--- a/lib/ai/backtrack.nit
+++ b/lib/ai/backtrack.nit
@@ -40,7 +40,7 @@ module backtrack
 # # Basic search
 #
 # The method `solve` returns a new solver for a backtrack search.
-class BacktrackProblem[S: Object,A]
+abstract class BacktrackProblem[S: Object,A]
        # The starting state of the problem.
        # It is this object that will be modified by `apply_action` and `backtrack`.
        fun initial_state: S is abstract