graph: make state of empty less contradictory and provide debugging strings
@@ -286,9 +286,9 @@ var (
_ WeightedLineSlicer = Empty
)
-const nothing = empty(true)
+const nothing = empty(0)
-type empty bool
+type empty int
func (empty) Next() bool { return false }
func (empty) Len() int { return 0 }
@@ -303,3 +303,6 @@ func (empty) Line() Line { return nil }
func (empty) LineSlice() []Line { return nil }
func (empty) WeightedLine() WeightedLine { return nil }
func (empty) WeightedLineSlice() []WeightedLine { return nil }
+
+func (empty) String() string { return "<empty>" }
+func (empty) GoString() string { return "graph.Empty" }
