Adding test and keeping validator API similar

include/CLI/Option.hpp

@@ -220,8 +220,13 @@ class Option : public OptionBase<Option> {
     }
 
     /// Adds a validator
-    Option *check(std::function<bool(std::string &)> validator) {
+    Option *check(std::function<bool(const std::string &)> validator) {
+        validators_.emplace_back(validator);
+        return this;
+    }
 
+    /// Adds a validator-like function that can change result
+    Option *transform(std::function<bool(std::string &)> validator) {
         validators_.push_back(validator);
         return this;
     }

include/CLI/Validators.hpp

@@ -19,7 +19,7 @@ namespace CLI {
 /// @defgroup validator_group Validators
 /// @brief Some validators that are provided
 ///
-/// These are simple `bool(std::string)` validators that are useful.
+/// These are simple `bool(std::string&)` validators that are useful.
 /// @{
 
 /// Check for an existing file

tests/AppTest.cpp

@@ -1171,3 +1171,23 @@ TEST_F(TApp, SetWithDefaultsIC) {
 
     EXPECT_THROW(run(), CLI::ConversionError);
 }
+
+// Added to test defaults on dual method
+TEST_F(TApp, OrderedModifingValidators) {
+    std::vector<std::string> val;
+    auto m = app.add_option("-m", val);
+    m->transform([](std::string &x) {
+        x += "1";
+        return true;
+    });
+    m->transform([](std::string &x) {
+        x += "2";
+        return true;
+    });
+
+    args = {"-mone", "-mtwo"};
+
+    run();
+
+    EXPECT_EQ(val, std::vector<std::string>({"one12", "two12"}));
+}