Add Element::hasTag method

Helpful during merging elements.

src/osm/element.cpp

@@ -111,6 +111,11 @@ QByteArray Element::tagValue(const char *keyName, const QLocale &locale) const
     return {};
 }
 
+bool Element::hasTag(TagKey key) const
+{
+    return std::binary_search(tagsBegin(), tagsEnd(), key);
+}
+
 std::vector<Tag>::const_iterator OSM::Element::tagsBegin() const
 {
     switch (type()) {

src/osm/element.h

@@ -50,6 +50,8 @@ public:
     template <typename K, typename ...Args> QByteArray tagValue(K key, Args... args, const QLocale &locale) const;
     /** Returns whether or not this element has any tags set. */
     inline bool hasTags() const { return std::distance(tagsBegin(), tagsEnd()) > 0; }
+    /** Returns @c true if this element has a tag with key @p key. */
+    bool hasTag(TagKey key) const;
 
     std::vector<Tag>::const_iterator tagsBegin() const;
     std::vector<Tag>::const_iterator tagsEnd() const;