From 96017dd7cdf43fa4b8f21c838affabfc6b0ccc23 Mon Sep 17 00:00:00 2001
From: Dean Moldovan <dean0x7d@gmail.com>
Date: Fri, 3 Jun 2016 10:00:40 +0200
Subject: [PATCH] Add _a literal for named arguments

---
 example/example11.cpp   |  3 +++
 example/example11.py    |  5 ++++-
 example/example11.ref   |  7 +++++++
 include/pybind11/attr.h | 20 +++++++++++++-------
 4 files changed, 27 insertions(+), 8 deletions(-)

diff --git a/example/example11.cpp b/example/example11.cpp
index 799fa6226..636a36ce1 100644
--- a/example/example11.cpp
+++ b/example/example11.cpp
@@ -55,4 +55,7 @@ void init_ex11(py::module &m) {
 
     m.def("args_function", &args_function);
     m.def("args_kwargs_function", &args_kwargs_function);
+
+    using namespace py::literals;
+    m.def("kw_func_udl", &kw_func, "x"_a, "y"_a=300);
 }
diff --git a/example/example11.py b/example/example11.py
index ff35be2e4..33ed80be3 100755
--- a/example/example11.py
+++ b/example/example11.py
@@ -6,12 +6,13 @@ import pydoc
 sys.path.append('.')
 
 from example import kw_func, kw_func2, kw_func3, kw_func4, call_kw_func
-from example import args_function, args_kwargs_function
+from example import args_function, args_kwargs_function, kw_func_udl
 
 print(pydoc.render_doc(kw_func, "Help on %s"))
 print(pydoc.render_doc(kw_func2, "Help on %s"))
 print(pydoc.render_doc(kw_func3, "Help on %s"))
 print(pydoc.render_doc(kw_func4, "Help on %s"))
+print(pydoc.render_doc(kw_func_udl, "Help on %s"))
 
 kw_func(5, 10)
 kw_func(5, y=10)
@@ -39,3 +40,5 @@ call_kw_func(kw_func2)
 
 args_function('arg1_value', 'arg2_value', 3)
 args_kwargs_function('arg1_value', 'arg2_value', arg3='arg3_value', arg4=4)
+
+kw_func_udl(x=5, y=10)
diff --git a/example/example11.ref b/example/example11.ref
index f4c23aecd..e965187ea 100644
--- a/example/example11.ref
+++ b/example/example11.ref
@@ -18,6 +18,11 @@ Help on built-in function kw_func4 in module example
 kkww__ffuunncc44(...)
     kw_func4(myList : list<int> = [13L, 17L]) -> NoneType
 
+Help on built-in function kw_func_udl in module example
+
+kkww__ffuunncc__uuddll(...)
+    kw_func_udl(x : int, y : int = 300L) -> NoneType
+
 kw_func(x=5, y=10)
 kw_func(x=5, y=10)
 kw_func(x=5, y=10)
@@ -40,3 +45,5 @@ got argument: arg1_value
 got argument: arg2_value
 got keyword argument: arg3 -> arg3_value
 got keyword argument: arg4 -> 4
+
+kw_func(x=5, y=10)
diff --git a/include/pybind11/attr.h b/include/pybind11/attr.h
index 5e2d8f2e0..d2525e5fc 100644
--- a/include/pybind11/attr.h
+++ b/include/pybind11/attr.h
@@ -18,23 +18,29 @@ template <typename T> struct arg_t;
 
 /// Annotation for keyword arguments
 struct arg {
-    arg(const char *name) : name(name) { }
-    template <typename T> arg_t<T> operator=(const T &value);
-    template <typename T, size_t N> arg_t<const T *> operator=(T const (&value)[N]);
+    constexpr arg(const char *name) : name(name) { }
+
+    template <typename T>
+    constexpr arg_t<T> operator=(const T &value) const { return {name, value}; }
+    template <typename T, size_t N>
+    constexpr arg_t<const T *> operator=(T const (&value)[N]) const {
+        return operator=((const T *) value);
+    };
+
     const char *name;
 };
 
 /// Annotation for keyword arguments with default values
 template <typename T> struct arg_t : public arg {
-    arg_t(const char *name, const T &value, const char *descr = nullptr)
+    constexpr arg_t(const char *name, const T &value, const char *descr = nullptr)
         : arg(name), value(value), descr(descr) { }
     T value;
     const char *descr;
 };
 
-template <typename T> arg_t<T> arg::operator=(const T &value) { return arg_t<T>(name, value); }
-template <typename T, size_t N> arg_t<const T *> arg::operator=(T const (&value)[N]) {
-    return operator=((const T *) value);
+inline namespace literals {
+/// String literal version of arg
+constexpr arg operator"" _a(const char *name, size_t) { return {name}; }
 }
 
 /// Annotation for methods