Add alias for const_iterator

Older generic code (e.g. before auto) might require
const_iterator, so provide it as an alias to iterator.

lib/coveo/enumerable/enumerable.h

@@ -42,6 +42,10 @@ class enumerable
     // Forward declaration of iterator class.
     class iterator;
 
+    // Even though begin() and end() are already const, some might want
+    // to use const_iterator, to let's create an alias.
+    typedef iterator        const_iterator;
+
 private:
     next_delegate zero_;    // Next delegate which we will clone to iterate sequence.
     size_delegate size_;    // Optional size delegate.
@@ -105,9 +109,16 @@ class enumerable
     iterator begin() const {
         return iterator(*this, false);
     }
+    iterator cbegin() const {
+        return begin();
+    }
+
     iterator end() const {
         return iterator(*this, true);
     }
+    iterator cend() const {
+        return end();
+    }
 
     // Access to size of sequence
     bool has_fast_size() const {

tests/coveo/enumerable/enumerable_tests.cpp

@@ -23,6 +23,12 @@ void validate_sequence(const coveo::enumerable<T>& seq, const C& expected, bool
         COVEO_ASSERT(obj == *eit++);
     }
     COVEO_ASSERT(eit == eend);
+    eit = std::begin(expected);
+    for (auto sit = seq.cbegin(), send = seq.cend(); sit != send; ++sit) {
+        COVEO_ASSERT(eit != eend);
+        COVEO_ASSERT(*sit == *eit++);
+    }
+    COVEO_ASSERT(eit == eend);
     COVEO_ASSERT(seq.has_fast_size() == fast_size);
     COVEO_ASSERT(seq.size() == expected.size());
 }