util/OptionParser: add struct Result

Prepare for option values.

src/CommandLine.cxx

@@ -309,9 +309,8 @@ ParseCommandLine(int argc, char **argv, struct options &options)
 
 	// First pass: handle command line options
 	OptionParser parser(option_defs, argc, argv);
-	int option_index;
-	while ((option_index = parser.Next()) >= 0) {
-		switch (Option(option_index)) {
+	while (auto o = parser.Next()) {
+		switch (Option(o.index)) {
 		case OPTION_KILL:
 			options.kill = true;
 			break;

src/util/OptionParser.cxx

@@ -23,7 +23,7 @@
 
 #include <string.h>
 
-inline unsigned
+inline OptionParser::Result
 OptionParser::IdentifyOption(const char *s) const
 {
 	assert(s != nullptr);
@@ -33,18 +33,18 @@ OptionParser::IdentifyOption(const char *s) const
 		for (const auto &i : options)
 			if (i.HasLongOption() &&
 			    strcmp(s + 2, i.GetLongOption()) == 0)
-				return &i - options.data;
+				return {int(&i - options.data)};
 	} else if (s[1] != 0 && s[2] == 0) {
 		const char ch = s[1];
 		for (const auto &i : options)
 			if (i.HasShortOption() && ch == i.GetShortOption())
-				return &i - options.data;
+				return {int(&i - options.data)};
 	}
 
 	throw FormatRuntimeError("Unknown option: %s", s);
 }
 
-int
+OptionParser::Result
 OptionParser::Next()
 {
 	while (!args.empty()) {
@@ -55,5 +55,5 @@ OptionParser::Next()
 		*remaining_tail++ = arg;
 	}
 
-	return -1;
+	return {-1};
 }

src/util/OptionParser.hxx

@@ -45,17 +45,22 @@ public:
 		 remaining_head(const_cast<const char **>(_argv + 1)),
 		 remaining_tail(remaining_head) {}
 
+	struct Result {
+		int index;
+
+		constexpr operator bool() noexcept {
+			return index >= 0;
+		}
+	};
+
 	/**
 	 * Parses current command line entry.
 	 * Regardless of result, advances current position to the next
 	 * command line entry. 
 	 *
 	 * Throws on error.
-	 *
-	 * @return the index if an option was found, -1 if there are
-	 * no more options
 	 */
-	int Next();
+	Result Next();
 
 	/**
 	 * Returns the remaining non-option arguments.
@@ -65,7 +70,7 @@ public:
 	}
 
 private:
-	unsigned IdentifyOption(const char *s) const;
+	Result IdentifyOption(const char *s) const;
 };
 
 #endif