# C++0x/C++11 support for SWIG

# Summary

This is a technical overview of the C++0x/C++11 support for the Swig. This area of Swig is a work in progress. Initial C++0x/C++11 support for Swig was written during the Google Summer of Code 2009 period by Matevž Jekovec.

# SVN branch

branches/gsoc2009-matevz

# New C++11 features status

Wikipedia article: http://en.wikipedia.org/wiki/C%2B%2B0x

## Rvalue reference and move semantics [done]

The Rvalues are used in practice to speed up the move operations on different containers.

In the following example, we want to swap the given elements:

    template <class T> swap(T& a, T& b) {
        T tmp(a);   // now we have two copies of a
        a = b;      // now we have two copies of b
        b = tmp;    // now we have two copies of tmp (aka a)
    }

This can now be solved using the new function std::move():

    template <class T> swap(T& a, T& b) {
        T tmp(std::move(a));
        a = std::move(b);
        b = std::move(tmp);
    }

For the move function to take effect, user needs to reimplement the move constructor (taking ClassType&& as an argument) and operator=(ClassType&&):

    class MyClass {
      MyClass(MyClass&& p) : ptr(p.ptr) {p.ptr = 0;}
      MyClass& operator=(MyClass&& p) {
        std::swap(ptr, p.ptr);
        return *this;
      }
    };

In practice, the Rvalues are used for temporaries (when passing the result of one function as an argument to another).

Done: Added type&& to Swig parser. Added testcase cpp11_rvalue_reference.i. Operator && is treated the same as operator &. R11450

Article: http://www.artima.com/cppsource/rvalue.html

## Generalized constant expressions [done]

In C++11 you can define functions as constant expressions. Functions need to return constant value in form "return expr", where expr is a constant expression.

A keyword "constexpr" is introduced for this. eg.: constexpr int getNumber() { return 5; } const int MY_CONSTANT = getNumber();

Constants are treated as normal variables in interpreted languages because they are not compiled into the executable. Java "final" constants are defined runtime as well. C++ constants need to be declared in the header file and defined in the implementation file, so swig doesn't need to know about the constant values when parsing the header file.

Done: Added the “constexpr “ keyword to Swig. Added testcase cpp11_constexpr. R11322

Problem: No compilers were known to support constexpr yet, so the testcase was temporarily commented out in common.mk.

## Extern template [done]

Extern template forces the GCC compiler to not instantiate the template in the translation unit at that time. It's a feature specifically aimed at compilers to speed up the compilation process.

Done: Added support for 'extern template class std::vector<MyClass>;'. Added testcase cpp11_template_explicit. R11385 , R11386

## Initializer lists [done]

Initializer list is a new type in standard library: std::initializer_list<T>. New symbols {} are introduced for the initializer lists.

One can now use:

     class A {
     public:
       A( std::initializer_list<int> );
     };
     A a1 = {1,2,3,4};

Languages like Java, C# and Python already support direct creation of lists natively.

Problem: initializer_list cannot be treated as an ordinary list. The constructor containing initializer_list can only be accessed by assigning the value using the {} brackets. I also don't think there is a simple way to convert an ordinary list or a vector to the initializer_list.

Done: Ignored the constructor having initializer_list as its argument. Show warning to the user. Added testcase cpp11_initializer_list. R11450

Article: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1919.pdf

## Uniform initialization [done]

The new C++11 standard will allow the following:

    struct IdString {
      std::string name;
      int identifier;
    };

    IdString GetString() {
      return {"SomeName", 4}; //Note the lack of explicit type.
    }

The feature works exactly as it did now for POD types only (eg. int a[] = {1,2,3};). The following declarations are the same in the new C++11:

    IdString str1 = {„SomeName“, 4};
    IdString str2{„SomeName“, 4};

The new way of using uniform initialization allows the following:

    struct BasicStruct {
     int x;
     double y;
    };

    struct AltStruct {
      AltStruct(int x, double y) : x_{x}, y_{y} {}

    private:
      int x_;
      double y_;
    };

    BasicStruct var1{5, 3.2}; // only fills the struct components
    AltStruct var2{2, 4.3};   // calls the constructor

The new syntax is specific to C++. Java, C# and scripting languages do not support this behaviour, but always need constructors. They support {} brackets for declaration of arrays as C does + they add support for creation of arrays on-the-fly (what C++11 introduced with this feature and more).

Done: Added syntax for {} member initialization in class constructor. Added testcase cpp11_uniform_initialization. R11413

## Type inference [partially done]

A new keyword 'auto' is introduced in C++11:

    auto a1 = 100;
    auto a2 = myFunc();

The type of a1 and a2 is automatically determined according to the initialization value during the semantic phase of the compiler.

Another macro 'decltype()' is introduced. The macro takes the concrete object as an argument and returns its type. User could use this as:

    int i = 100;
    decltype(i) j = 200; // decltype(i) = int

Calling operators are allowed as well:

    decltype(i+j) k = 300;

Done: Added support for decltype() syntax. Test cases for normal decltype members and alternate function members work fine. Currently only syntax in form decltype(variable name) work. No support for custom expresions eg. decltype(i+j) yet. R11525

TODO: William proposed to support the hidden variables as well (ones not parsed by Swig and added to symbol table). This also allows Swig to parse custom expressions like decltype(i+j). The idea is to introduce a new SwigType for this.

## Range-based for-loop [ignored]

This feature is always present inside the implementation block only.

## Lambda functions and expressions [done]

C++11 introduces lambda functions defined as:

    [](int x, int y) -> int { return x + y; }

If the lambda function contains a single return statement only or the function doesn't return any type, the return type '->' can be omitted. Lambda functions are function objects.

The following example prints the number of items stored in a list:

    std::vector<int> someList;
    int total = 0;
    std::for_each( someList.begin(), someList.end(), [&total](int x) {total += x} );
    std::cout << total;

Parameters inside the [] are the visible parameters of the lambda functions. These can be & (references), = (copies), variable name (variable copy), &variable name (variable reference) or this (copy of the current object).

Lambda functions can be stored using:

    auto myLambdaFunc = [this]() { this->SomePrivateMemberFunction() };

Proposal: Lambda functions are most commonly used inside the function block to quickly define how the sort, find and similar functions should work (the other way would be overriding a class – the Java style). The latest GCC does not support lambda functions yet so it is difficult to test the feature once implemented. I would implement the syntax support for this feature, but produce no wrapper code. Lambda functions still work inside the function block though.

Article: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2550.pdf

Done: Added syntax support for the lambda functions. Added testcase cpp11_lambda_functions.i. R11491, R11492

## Alternate function syntax [done]

The problem with decltype() is that the parameters need to be defined before the decltype. The following syntax is not valid, because lhs and rhs hasn't been defined at the time of decltype:

    template< typename LHS, typename RHS>
      decltype(lhs+rhs) AddingFunc(const LHS &lhs, const RHS &rhs) {return lhs + rhs;} //Not legal C++11

The solution C++11 offers is the combination of the 'auto' keyword before and '-> rettype' after the function declaration:

    template< typename LHS, typename RHS>
      auto AddingFunc(const LHS &lhs, const RHS &rhs) -> decltype(lhs+rhs) {return lhs + rhs;}

The new syntax only makes the job for the C++ compilers easier when parsing such functions. The new syntax can be used for ordinary functions as well:

    struct SomeStruct {
      auto FuncName(int x, int y) -> int;
    };

    auto SomeStruct::FuncName(int x, int y) -> int {
      return x + y;
    }

Done: Added support for the 'auto' return type. Added support for the '-> type' after the funtion declaration. Added testcases cpp11_alternate_function_syntax.i and cpp11_alternate_function_syntax_runme.py. R11414

## Concepts, Axioms [ignored]

In C++ there is a common problem when you use a template in the class which doesn't support all the operations the functions in the class actually do on the type. Compiler errors are usually very long and unreadable. C++11 adds support for the "concepts". The idea is to define what operations and attributes should the template have. In contrast to class inheritance and polimorphism, all lookups are done in compile-time.

Basic syntax (note LessThanComparable? instead of "class" or "typename"):

     template<LessThanComparable? T>
     const T& min(const T &x, const T &y) {
       return y < x ? y : x;
     }

Extended syntax (requires conditions are separated with &&, || or !):

     template< typename T> requires LessThanComparable?<T>
     const T& min(const T &x, const T &y) {
       return y < x ? y : x;
     }

Definition of the concepts:

     concept LessThanComparable?< typename T > {
       bool operator<(T,T);
       requires GreaterThanComparable?<T>;
       typename value_type;
       typename reference;
     };

Concept maps allow usage of a specific type:

     template< typename T>
     concept_map InputIterator?<T*> {
       typedef T value_type ;
       typedef T& reference ;
       typedef T* pointer ;
       typedef std::ptrdiff_t difference_type ;
     };

Concept maps can act as mini-types, with function definitions and other constructs commonly associated with classes:

     concept Stack< typename X> {
       typename value_type;
       void push(X&, const value_type&);
       void pop(X&);
       value_type top(const X&);
       bool empty(const X&);
     };
     template< typename T>
     concept_map Stack<std::vector<T> > {
       typedef T value_type;
       void push(std::vector<T>& v, const T& x) { v.push_back(x); }
       void pop(std::vector<T>& v) { v.pop_back(); }
       T top(const std::vector<T>& v) { return v.back(); }
       bool empty(const std::vector<T>& v) { return v.empty(); }
     };

Axioms are a facility pertaining to concepts supplied by C++11 to express the semantic properties of concepts. For example, the concept Semigroup can be defined with an axiom Associativity as:

     concept Semigroup< typename Op, typename T> : CopyConstructible?<T> {
       T operator()(Op, T, T);
       axiom Associativity(Op op, T x, T y, T z) {
         op(x, op(y, z)) == op(op(x, y), z);
       }
     };

Axioms are more like hints to the compiler to speed-up the process of compilation.

Ignored: Concepts and axioms were removed from the C++11 standard.

## Object construction improvement [done]

This feature allows classes constructors to call other constructors with different arguments (similar to Java and C# behaviour).

The syntax is as follows:

     class SomeType {
      int number;
     public:
       SomeType(int newNumber) : number(newNumber) {}
       SomeType() : SomeType(42) {}
     };

Also when using the inheritance, the feature introduces inheritance of all superclass constructors without being defined separately in the inherited class:

     class BaseClass {
     public:
       BaseClass(int iValue);
     };
     class DerivedClass: public BaseClass {
       public:
       using BaseClass::BaseClass; // Adds DerivedClass(int) constructor
     };

Swig already correctly parses and produces the correct wrapper for the “using” keyword.

Done: Added testcase cpp11_constructors.i which covers both constructor delegation and constructor inheritance. R11532

Problem: Constructor delegation and constructor inheritance is not supported by any compiler yet, so it's impossible to try and test this feature.

## Null pointer constant [done]

nullptr is part of the standard library.

It's defined as typedef decltype(nullptr) nullptr_t;

nullptr_t is defined in <cstddef>.

As far as the C++ is compatible with 0 as the pointer value, swig values will work for the C++. And the other way around, nullptr behaves as the ordinary pointer (false, if empty, true, if not empty), so it's ok for swig to compare it.

Done: Written a testcase cpp11_null_pointer_constant.i and cpp11_null_pointer_constant_runme.py to prove the nullptr functionality. R11484

## Strongly typed enumerations [partially done]

C++11 introduces a new syntax for strongly typed enum declaration:

     enum class Enumeration {
      Val1,
      Val2,
      Val3 = 100,
      Val4 /* = 101 */
     };

Typing if (Val4 == 101) will result in compilation error.

The enum itself can now be explicitely of type int, long, unsigned int etc.:

     enum class Enum2 : unsigned int {Val1, Val2};

And it can be forward declared as well:

     enum Enum1;                   //Illegal in C++ and C++11; no size is explicitly specified.
     enum Enum2 : unsigned int;    //Legal in C++11.
     enum class Enum3;             //Legal in C++11, because enum class declarations have a default type of "int".
     enum class Enum4: unsigned int; //Legal C++11.
     enum Enum2 : unsigned short;  //Illegal in C++11, because Enum2 was previously declared with a different type.

Done: Added syntax 'enum class Name' and forward declarators 'enum Name : inherited type' or 'enum class Name : inherited type' in R11449.

TODO: Add semantic support for enum elements not clashing with enum elements in other enum classes. See cpp11_strongly_typed_enums.i warnings.

Problem: Swig currently doesn't support nested classes. This feature should be implemented using a new nested class when using “enum class” with a single anonymous “enum {elements}” element inside. For example:

    class A { enum class EA { a,b,c,d }; };

should be mapped to

    class A { class EA { enum {a,b,c,d}; }; };

## Angle bracket [done]

Support for right angled brackets was implemented using the following article as a base: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1757.html

Done: Added support for angle brackets. Used the preferred "Approach 1". Added a testcase named cpp11_template_double_brackets. R11245

## Explicit conversion operators [done]

This is used when converting one type to another (eg. if (myObject) {}, where myObject is your custom class converted to bool).

Requires both operator and function overloading which is not supported in any target language (eg. python, php).

Done: Swig already supports the keyword "explicit" for function types as well. Added test case cpp11_explicit_conversion_operators. R11323

## Template typedefs [partially done]

The new C++11 will allow creation of wrapper around the template. For example, if we want to do this:

    template< typename first, typename second, int third>
    class SomeType;

    template< typename second>
    typedef SomeType<OtherType, second, 5> TypedefName; //Illegal in C++

This is still illegal! But we can now use the new syntax for achieving the same effect:

    template< typename first, typename second, int third>
    class SomeType;

    template< typename second>
    using TypedefName = SomeType<OtherType, second, 5>;

Here we created a new wrapper TypedefName taking one template argument <second> which creates a type SomeType<OtherType, second, 5>. OtherType and 5 are predefined here and hidden from the user – the user only uses TypedefName type.

The same goes for the following example:

    typedef void (*PFD)(double);            // Old style
    using PF = void (*)(double);            // New introduced syntax

Swig supports parsing typedefs for templates as well for example:

    typedef List<int> intList;

Done: Expanded support for the new 'using' syntax and template aliasing. Added testcase cpp11_template_typedefs. R11533

TODO: Make Swig aware of the newly defined typedef. The TYPEDEF keyword is part of the storage_class rule and type+declarator (see c_decl rule) is the right part of the definition – for example void (*PFD)(double) cannot be transformed to void *(double) easily. To fully support the new 'using' form, we'll probably have to change the type, type_right rules and declarator, direct_declarator, notso_direct_declarator etc., which is PITA.

## Unrestricted unions [done]

C++ currently offers usage of unions for types with trivial constructors only. The new C++11 standard allows usage of types with non-trivial constructors as well:

     struct point {
      point() {}
      point(int x, int y): x_(x), y_(y) {}
      int x_, y_;
     };
     union P {
      int z;
      double w;
      point p;  // Illegal in C++; point has a non-trivial constructor.  However, this is legal in C++11.
     } p1;

Swig already parses the given syntax.

Done: Added testcase cpp11_unrestricted_unions. R11435, R11447

Problem: GCC doesn't support unrestricted unions yet so there is no way to actually test, if it works.

## Variadic templates [partially done]

The new C++11 offers the following syntax:

    template<typename... Values> class tuple;

This can be used for example:

    class tuple<int, std::vector<int>, std::map<std::string, std::vector<int>>> someInstanceName;

The ... is used in two cases. One is in the template header where it marks on the left the keywords 'typename' or 'class' and a type name on the right. The second case is usually in the function block to decompose typename on the left of the ... . For example:

    void printf(const char *s) {
      while (*s) {
        if (*s == '%' && *(++s) != '%')
          throw std::runtime_error("invalid format string: missing arguments");
        std::cout << *s++;
      }
    }

    template<typename T, typename... Args>
    void printf(const char* s, T value, Args... args) { // recursive action – split previous args to value + args
      while (*s) {
        if (*s == '%' && *(++s) != '%') {
          std::cout << value;
          printf(*s ? ++s : s, args...); // call even when *s == 0 to detect extra arguments
          return;
        }
        std::cout << *s++;
      }
      throw std::logic_error("extra arguments provided to printf");
    }

The tricky part is that variadic templates can unpack actually anywhere – including the class inheritance :(

    template <typename... BaseClasses> class ClassName : public BaseClasses... {
    public:

       ClassName (BaseClasses&&... baseClasses) : BaseClasses(baseClasses)... {}
    }

A new extension to sizeof is also introduced with this feature. The ... after sizeof returns number of arguments:

    template<typename ...Args> struct SomeStruct {
      static const int size = sizeof...(Args);
    }
    // SomeStruct<Type1, Type2>::size is 2 and SomeStruct<>::size is 0

Done: Added syntax support for 'typename' or 'class' + ... + id. Added testcase cpp11_variadic_templates. R11458

Done: Added syntax support for BaseClass + ..., type + ... + id in parameters and baseclass + ... for intializers after constructor. Extended Swig syntax to support sizeof...(Args). R11467

Done: Fixed %template to support variadic number of templates.

TODO: Only (if present) first variadically defined argument is currently used in %template directive. The next ones are ignored.

## New string literals [partially done]

Beside the implementation, the new C++11 Unicode and custom delimeter constants can occur in templates in the header file.

Done: Added symbols 'u', 'u8' and 'U' to mark the beginning of the UTF string. Also added test case cpp11_raw_string_literals. R11327

Done: Added R"DELIMITER[, ]DELIMITER" for a custom delimiter for the beginning/end of the string. R11328

TODO: Fix the Swig's C++ preprocessor bug when parsing an odd number of “ inside the string brackets. See Source/Preprocessor/cpp.c.

## User-defined literals [partially done]

C++ has different suffix literals. eg. 12.5f marks the number 12.5 as float.

C++11 allows user to define his own suffix for the strings always starting with the underscore (_). eg. int a = "hello"_mySuffix;

The syntax is similar to other operator overloading functions:

     OutputType operator "" _mySuffix(const char * string_values);

The null terminated const char* is the string between the "". The _mySuffix is the name of the suffix operator. And the OutputType is the outputType the operator returns.

Other forms are:

     OutputType operator "" _mySuffix(const char * string_values, size_t num_chars);
     OutputType operator "" _mySuffix(const wchar_t * string_values, size_t num_chars);
     OutputType operator "" _mySuffix(const char16_t * string_values, size_t num_chars);
     OutputType operator "" _mySuffix(const char32_t * string_values, size_t num_chars);
     OutputType operator "" _mySuffix(int value); /* cooked version - ie. atoi() of string */

Another possibility is to use variadic templates:

     template<char...> OutputType operator "" _mySuffix();
     OutputType someVariable = "1234"_mySuffix;

This instantiates the literal processing function as operator""_Suffix<'1', '2', '3', '4'>. In this form, there is no terminating null character to the string. The main purpose to doing this is to use C++11's constexpr keyword and the compiler to allow the literal to be transformed entirely at compile time, assuming OutputType is a constexpr-constructable and copyable type, and the literal processing function is a constexpr function.

Article: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2765.pdf

Done: Added syntax support for userdefined literals. Added testcase cpp11_userdefined_literals.i. R11494

TODO: %rename doesn't parse operator”” yet.

## Thread-local storage [done]

New C++11 introduces keyword "thread_local" which marks the following variable dynamically located depending on the current thread when using the address-of (&) operator.

Syntax:

     struct A {
       thread_local int val;
     };

Done: Add "thread_local" keyword to Swig. Added testcase cpp11_thread_local. R11393

## Defaulting/deleting of standard functions on C++ objects [done]

C++ automatically creates default constructor with empty parameters, copy constructor, operator= and destructor for any class. Sometimes user wants to explicitly remove one of them or enable them (eg. default constructor with empty parameters doesn't work any more, if any other constructor is defined).

Words "default" and "delete" are introduced. The syntax is similar to declaration of pure virtual function:

     struct NonCopyable {
       NonCopyable & operator=(const NonCopyable&) = delete; /* Removes operator= */
       NonCopyable(const NonCopyable&) = delete; /* Removed copy constructor */
       NonCopyable() = default; /* Explicitly allows the empty constructor */
       void *operator new(std::size_t) = delete; /* Removes new NonCopyable */
     };

User has the ability by using keyword delete to disallow calling of the standard functions brought by C++ itself.

     struct A1 {
       void f(int i);
       void f(double i) = delete;  /* Don't cast double to int. Compiler returns an error */
     };
     struct A2 {
       void f(int i);
       template<class T> void f(T) = delete; /* Only accept int */
     };

Ignored: Swig already parses the keywords "= delete" and "= default". These keywords are used for built-in functions (copy constructor, operator= etc.), which are ignored by Swig anyway.

Done: Added testcase cpp11_default_delete. R11535

## Type long long int [done]

Type long long int is an integer type that has at least 64 useful bits. C99 added it to its standard, but the C++ didn't adopt it until C++11. Most C++ compilers supported it though.

Done: Swig already parses the C code including the long long type.

## Static assertions [done]

static_assert() can be used at class scope as well eg.:

     template <typename T>
     struct Check {
      static_assert(sizeof(int) <= sizeof(T), "not big enough");
     };

Done: Added syntax support for "static_assert()". Added test case cpp11_static_assert. R11369

## Allow sizeof to work on members of classes without an explicit object [done]

C++11 allows calls of sizeof to concrete objects as well:

     struct A { int member; };
     sizeof(A::member); //Does not work with C++03. Okay with C++11

This kind of syntax is already supported by Swig.

Done: Added testcase cpp11_sizeof_objects. R11538

## Threading facilities [ignored]

C++11 will add the following classes to the standard library:

     * std::thread
     * std::mutex, std::recursive_mutex
     * std::condition_variable, std::condition_variable_any
     * std::lock_guard, std::unique_lock
     * std::packaged_task

Ignored: No changes to the language itself is made.

## Tuple types [TODO]

Tuple is array of various types. C++11 introduced this feature using variadic templates. Tuple is defined as:

    template <class ...Types> class tuple;

Constructor is automatically generated filling the tuple elements. get<X> function is introduced to get the Xth element in the tuple.

    typedef tuple< int, double, long &, const char * > test_tuple ;
    long lengthy = 12 ;
    test_tuple proof( 18, 6.5, lengthy, "Ciao!" ) ;
    lengthy = get<0>(proof) ;  // Assign to 'lengthy' the value 18.
    get<3>(proof) = " Beautiful!" ;  // Modify the tuple’s fourth element.

Tuples can be copied to each other, if all the elements are copiable:

    typedef tuple< int , double, string       > tuple_1 t1 ;
    typedef tuple< char, short , const char * > tuple_2 t2( 'X', 2, "Hola!" ) ;
    t1 = t2 ;  // Ok, first two elements can be converted,
               // the third one can be constructed from a 'const char *'.

TODO: Implement wrappers for the tuplet<> class.

## Hash tables [TODO]

C++11 introduces the "unordered" version of existing types, which in practice work faster than the linear types:

     - unordered set
     - unordered multiset
     - unordered map
     - unordered multimap

Swig should use the "unordered" types exactly the same as the original linear types.

Problem: Unordered types do not contain exactly same members as ordered ones (eg. _Hashtable_iterator does not offer operator--() and constructor with compare function which is required). So simply aliasing unordered classes to ordered ones doesn't work.

TODO: Implement wrappers for unordered_ types. Initial work is already done in Lib/std/unordered_*.i files.

## Regular expressions [ignored]

Two new classes are introduced in C++11: basic_regex and match_results. Both are defined in regex header file.

Ignored: The new feature extends the standardy library only. No changes to Swig needed.

## General-purpose smart pointers [done]

This feature deprecates auto_ptr and adds shared_ptr, weak_ptr and unique_ptr to the standard library.

This feature only adds the smart pointers to the standard library and doesn't effect the C++ syntax.

Done: Added test case which uses all three smart pointers in the class. R11394

Problem: GCC standard library doesn't contain the new smart pointers yet.

## Extensible random number facility [ignored]

This feature standardize the pseudo random number algorithm (currently, the random number generator was dependent on the platform/compiler). It adds functions linear_congruential, subtract_with_carry and mersenne_twister and symbols uniform_int_distribution, bernoulli_distribution, geometric_distribution, poisson_distribution, binomial_distribution, uniform_real_distribution, exponential_distribution, normal_distribution and gamma_distribution to the standard library.

Ignored: The new feature extends the standardy library only. No changes to Swig needed.

## Wrapper reference [ignored]

This feature adds ref and cref classes to the standard library (#include <utility>) usually used in tempalte functions.

Ignored: The new feature extends the standardy library only. No changes to Swig needed.

## Polymorphous wrappers for function objects [done]

Two features are introduced:

- The function template wrapper:

     function<int ( int, int )> pF;

- and the function object:

     struct Test {
       bool operator()( short x, short y );
     };

Swig already supports the two.

Done: Added a runtime testcase for function objects cpp11_function_objects. R11419.

## Type traits for metaprogramming [ignored]

C++11 adds a new header file <type_traits> which includes helper functions to determine the template type while initializing the object at compile time.

Swig already supports the following code:

     template< int B, int N >
     struct Pow {
      // recursive call and recombination.
      enum{ value = B*Pow< B, N-1 >::value };
     };
     template< int B > struct Pow< B, 0 >  // N == 0 condition of termination.
     {
      enum{ value = 1 };
     };
     int quartic_of_three = Pow< 3, 4 >::value ;

Functions is_convertible, is_integral, is_integral_const etc. are part of the new header:

    // First way of operating.
    template< bool B > struct algorithm {
      template< class T1, class T2 > int do_it( T1 &, T2 & )  { /*...*/ }
    };
    // Second way of operating.
    template<> struct algorithm<true> {
      template< class T1, class T2 > int do_it( T1, T2 )  { /*...*/ }
    };
    // Instantiating 'elaborate' will automatically instantiate the correct way to operate.
    template< class T1, class T2 > int elaborate( T1 A, T2 B ) {
      // Use the second way only if 'T1' is an integer and if 'T2' is
      // in floating point, otherwise use the first way.
      return algorithm< is_integral<T1>::value && is_floating_point<T2>::value >::do_it( A, B );
    }

Swig correctly parses the syntax for template<bool>, template<class T> and template<>.

Ignored: Swig requires explicitly defined template class (%template directive) to export it to the target language.

## Uniform method for computing return type of function objects [partially done]

The template function is introduced: std::result_of() which depends on decltype:

    template< class Obj >
    class calculus_ver2 {
     public:
       template< class Arg >
       typename std::result_of<Obj(Arg)>::type operator()( Arg& a ) const {
         return member(a);
       }
     private:
       Obj member;
    };

Swig correctly parses the result_of class.

TODO: The return type (the result_of::type member) is not calculated by Swig. This needs a much more complex semantic parser.

Done: Added testcase cpp11_result_of. R11534