Make method provider_options::for_each() const

Also, add a comment for the method and fix formatting

Author: sciascid

include/wsrep/provider_options.hpp

@@ -253,7 +253,13 @@ namespace wsrep
                     std::unique_ptr<option_value> value,
                     std::unique_ptr<option_value> default_value, int flags);
 
-        void for_each(const std::function<void(option*)>& fn);
+        /**
+         * Invoke the given function with each provider option
+         * as argument.
+         *
+         * @param fn Function to call for each option
+         */
+        void for_each(const std::function<void(option*)>& fn) const;
 
     private:
         using options_map = std::map<std::string, std::unique_ptr<option>>;

src/provider_options.cpp

@@ -161,9 +161,10 @@ enum wsrep::provider::status wsrep::provider_options::set_default(
     return wsrep::provider::success;
 }
 
-void wsrep::provider_options::for_each(const std::function<void(option*)>& fn)
+void wsrep::provider_options::for_each(
+    const std::function<void(option*)>& fn) const
 {
-    std::for_each(
-        options_.begin(), options_.end(),
-        [&fn](const options_map::value_type& opt) { fn(opt.second.get()); });
+    std::for_each(options_.begin(), options_.end(),
+                  [&fn](const options_map::value_type& opt)
+                  { fn(opt.second.get()); });
 }