Modifies combinations_with_replacement(c, 0) to produce {{}}

Issue #101

Author: Ryan Haining

combinations_with_replacement.hpp

@@ -60,6 +60,12 @@ class iter::impl::CombinatorWithReplacement {
                      ? 0
                      : COMPLETE} {}
 
+    static Iterator zero_length_end(ContainerT& container) {
+      Iterator it{container, 0};
+      it.steps_ = 0;
+      return it;
+    }
+
     CombIteratorDeref<ContainerT>& operator*() {
       return indices_;
     }
@@ -69,15 +75,19 @@ class iter::impl::CombinatorWithReplacement {
     }
 
     Iterator& operator++() {
+      if (indices_.get().empty()) {
+        // zero-length case.
+        ++steps_;
+        return *this;
+      }
       for (auto iter = indices_.get().rbegin(); iter != indices_.get().rend();
            ++iter) {
         ++(*iter);
         if (!(*iter != get_end(*container_p_))) {
           if ((iter + 1) != indices_.get().rend()) {
-            for (auto down = iter; ; --down) {
+            for (auto down = iter;; --down) {
               (*down) = dumb_next(*(iter + 1));
-              if (down == indices_.get().rbegin())
-                break;
+              if (down == indices_.get().rbegin()) break;
             }
           } else {
             steps_ = COMPLETE;
@@ -117,6 +127,9 @@ class iter::impl::CombinatorWithReplacement {
   }
 
   Iterator<Container> end() {
+    if (length_ == 0) {
+      return Iterator<Container>::zero_length_end(container_);
+    }
     return {container_, 0};
   }
 
@@ -125,6 +138,9 @@ class iter::impl::CombinatorWithReplacement {
   }
 
   Iterator<AsConst<Container>> end() const {
+    if (length_ == 0) {
+      return Iterator<AsConst<Container>>::zero_length_end(container_);
+    }
     return {std::as_const(container_), 0};
   }
 };

test/test_combinations_with_replacement.cpp

@@ -1,5 +1,4 @@
 #include <combinations_with_replacement.hpp>
-
 #include <iterator>
 #include <set>
 #include <string>
@@ -96,8 +95,23 @@ TEST_CASE("combinations_with_replacement: big size is no problem",
 TEST_CASE("combinations_with_replacement: 0 size is empty",
     "[combinations_with_replacement]") {
   std::string s{"A"};
-  auto cwr = combinations_with_replacement(s, 0);
-  REQUIRE(std::begin(cwr) == std::end(cwr));
+  CharCombSet sc;
+  for (auto v : combinations_with_replacement(s, 0)) {
+    sc.emplace_back(std::begin(v), std::end(v));
+  }
+  CharCombSet ans = {{}};
+  REQUIRE(ans == sc);
+}
+
+TEST_CASE("combinations_with_replacement: 0 size is empty with empty container",
+    "[combinations_with_replacement]") {
+  std::string s{};
+  CharCombSet sc;
+  for (auto v : combinations_with_replacement(s, 0)) {
+    sc.emplace_back(std::begin(v), std::end(v));
+  }
+  CharCombSet ans = {{}};
+  REQUIRE(ans == sc);
 }
 
 TEST_CASE("combinations_with_replacement: operator->",