Added operator- member implementation and improved test cases

* operator- takes a reference to a const std::string::const_iterator and as such enables determining the actual position of a codepoint within a string
* ranged for loops in test cases now take the iterator value by rvalue reference instead of by value

1 files changed, 5 insertions, 0 deletions

diff --git a/src/codepoint_iterator.cc b/src/codepoint_iterator.cc
index b2f6d81..59cb23b 100644
--- a/src/codepoint_iterator.cc
+++ b/src/codepoint_iterator.cc
@@ -34,6 +34,11 @@ bool CodepointIterator::operator!=(
 	return this->iterator_ != src;
 }
 
+std::ptrdiff_t CodepointIterator::operator-(
+	const std::string::const_iterator& src) const {
+	return this->iterator_ - src;
+}
+
 char32_t CodepointIterator::operator*() {
 	std::uint8_t  currByte  = *(this->iterator_);
 	char32_t codePoint      = 0;