comments from review

Author: mcognetta

src/operators.jl

@@ -904,23 +904,21 @@ julia> collect(edges(m))
 ```
 """
 @traitfn function mycielski(g::AbstractGraph::(!IsDirected); iterations = 1)
-    ref = g
     out = deepcopy(g)
     for _ in 1:iterations
-        N = nv(g)
+        N = nv(out)
         add_vertices!(out, N + 1)
         w = nv(out)
-        for e in collect(edges(g))
-            x, y = Tuple(e)
-            add_edge!(out, x, y)
+        for e in collect(edges(out))
+            x=e.src
+            y=e.dst
             add_edge!(out, x, y+N)
             add_edge!(out, x+N, y)
         end
 
         for v in 1:N
             add_edge!(out, v+N, w)
         end
-        g = out
     end
     return out
 end

test/operators.jl

@@ -329,11 +329,19 @@
         @test nv(m) == 767
         @test ne(m) == 22196
 
+        # ensure it is not done in-place
+        @test nv(g) == 2
+        @test ne(g) == 1
+
         # check that mycielski preserves triangle-freeness
         g = complete_bipartite_graph(10, 5)
         m = mycielski(g)
         @test nv(m) == 2*15 + 1
         @test ne(m) == 3*50 + 15
         @test all(iszero, triangles(m))
+
+        # ensure it is not done in-place
+        @test nv(g) == 15
+        @test ne(g) == 50
     end
 end