feat: Allow implicit values with disabled arguments

README.md

@@ -194,6 +194,16 @@ though it was given on the command line.
 
 Default values are not counted by `Options::count`.
 
+### Implicit values with disabled arguments
+
+You can specify an option for which an argument cannot be specified using below syntax.
+
+```cpp
+cxxopts::value<bool>()->implicit_value("true", true)
+```
+
+In this case specifying option as `--option=<value>` is disallowed and will throw `specified_disabled_args` exception. Note that `--option value` is not supported for implicit values. It is treated as positional/unmatched.
+
 ## Boolean values
 
 Boolean options have a default implicit value of `"true"`, which can be

include/cxxopts.hpp

@@ -394,6 +394,9 @@ class Value : public std::enable_shared_from_this<Value>
   virtual bool
   has_implicit() const = 0;
 
+  virtual bool
+  has_disabled_args() const = 0;
+
   virtual std::string
   get_default_value() const = 0;
 
@@ -404,7 +407,7 @@ class Value : public std::enable_shared_from_this<Value>
   default_value(const std::string& value) = 0;
 
   virtual std::shared_ptr<Value>
-  implicit_value(const std::string& value) = 0;
+  implicit_value(const std::string& value, bool disabled_args = false) = 0;
 
   virtual std::shared_ptr<Value>
   no_implicit_value() = 0;
@@ -482,6 +485,15 @@ class invalid_option_syntax : public parsing {
   }
 };
 
+class specified_disabled_args : public parsing {
+  public:
+  explicit specified_disabled_args(const std::string& text)
+  : parsing("Option " + LQUOTE + text + RQUOTE +
+            " has disabled_args but argument was specified")
+  {
+  }
+};
+
 class no_such_option : public parsing
 {
   public:
@@ -1271,6 +1283,12 @@ class abstract_value : public Value
     return m_implicit;
   }
 
+  bool
+  has_disabled_args() const override
+  {
+    return m_disabled_args;
+  }
+
   std::shared_ptr<Value>
   default_value(const std::string& value) override
   {
@@ -1280,10 +1298,11 @@ class abstract_value : public Value
   }
 
   std::shared_ptr<Value>
-  implicit_value(const std::string& value) override
+  implicit_value(const std::string& value, bool disabled_args = false) override
   {
     m_implicit = true;
     m_implicit_value = value;
+    m_disabled_args = disabled_args;
     return shared_from_this();
   }
 
@@ -1328,6 +1347,7 @@ class abstract_value : public Value
 
   bool m_default = false;
   bool m_implicit = false;
+  bool m_disabled_args = false;
 
   std::string m_default_value{};
   std::string m_implicit_value{};
@@ -2634,6 +2654,9 @@ OptionParser::parse(int argc, const char* const* argv)
           {
             //it must be the last argument
             if (argu_desc.set_value) {
+              if(value->value().has_disabled_args()){
+                throw_or_mimic<exceptions::specified_disabled_args>(name);
+              }
               parse_option(value, name, argu_desc.value);
             }
             else{
@@ -2681,6 +2704,9 @@ OptionParser::parse(int argc, const char* const* argv)
         //equals provided for long option?
         if (argu_desc.set_value)
         {
+          if(opt->value().has_disabled_args()){
+            throw_or_mimic<exceptions::specified_disabled_args>(name);
+          }
           //parse the option given
 
           parse_option(opt, name, argu_desc.value);

test/options.cpp

@@ -638,6 +638,66 @@ TEST_CASE("Boolean without implicit value", "[implicit]")
   }
 }
 
+TEST_CASE("Implicit value with disabled_args", "[no_value]")
+{
+  const char prog_name[] = "disabled_args";
+  cxxopts::Options options(prog_name, "Implicit value with disabled args");
+  options.add_options()
+    ("b,bool", "description", cxxopts::value<bool>()->implicit_value("true", true))
+    ("s,string", "description", cxxopts::value<std::string>()->implicit_value("value", true));
+  struct testcase{
+    std::string name;
+    Argv argv;
+  } tests_eq[] = {
+    {
+      "exception due to value passed in long arg",
+      Argv{prog_name, "--bool=true"},
+    },
+    {
+      "exception due to value passed in short arg",
+      Argv{prog_name, "-b=true"},
+    },
+    {
+      "exception due to string value",
+      Argv{prog_name, "-b", "--string=something_else"},
+    }
+  };
+
+  for(const auto& tc : tests_eq) {
+    SECTION(tc.name){
+      CHECK_THROWS_AS(options.parse(tc.argv.argc(), tc.argv.argv()),
+        cxxopts::exceptions::specified_disabled_args);
+    }
+  }
+
+  SECTION("unmatched string value without ="){
+    Argv argv{prog_name, "--string", "new_value"};
+    auto result = options.parse(argv.argc(), argv.argv());
+    CHECK(result.unmatched().size() == 1);
+    CHECK(result.unmatched()[0] == "new_value");
+    CHECK(result["string"].as<std::string>() == "value");
+  }
+  SECTION("unmatched short value without ="){
+    Argv argv{prog_name, "-s", "new_value"};
+    auto result = options.parse(argv.argc(), argv.argv());
+    CHECK(result.unmatched().size() == 1);
+    CHECK(result.unmatched()[0] == "new_value");
+    CHECK(result["string"].as<std::string>() == "value");
+  }
+  SECTION("exception due to short value grouped"){
+    Argv argv{prog_name, "-snew_value"};
+    // it will be considered as -s -n -e ... because -s has implicit value
+    CHECK_THROWS_AS(options.parse(argv.argc(), argv.argv()),
+      cxxopts::exceptions::no_such_option);
+  }
+  SECTION("No exception"){
+    Argv argv{prog_name, "--string", "-b"};
+    auto result = options.parse(argv.argc(), argv.argv());
+    CHECK(result["bool"].as<bool>() == true);
+    CHECK(result["string"].as<std::string>() == "value");
+  }
+}
+
 TEST_CASE("Default values", "[default]")
 {
   cxxopts::Options options("defaults", "has defaults");