Implement few builtin functions that can operate on any value

type()
null()
empty ()
identity()

4 files changed, 38 insertions, 1 deletions

diff --git a/build2/buildfile b/build2/buildfile
index fa6faef..98494d8 100644
--- a/build2/buildfile
+++ b/build2/buildfile
@@ -15,6 +15,7 @@ exe{b}:                                                 \
             {hxx ixx     cxx}{ file                   } \
             {hxx     txx cxx}{ filesystem             } \
             {hxx         cxx}{ function               } \
+            {            cxx}{ functions-builtin      } \
             {            cxx}{ functions-path         } \
 	    {            cxx}{ functions-process-path } \
             {hxx         cxx}{ lexer                  } \
diff --git a/build2/function b/build2/function
index 68edcde..192c4a3 100644
--- a/build2/function
+++ b/build2/function
@@ -37,7 +37,8 @@ namespace build2
   // T           - statically-typed (value_traits<T> must be defined)
   // names       - untyped
   // value       - any type
-  // T*          - NULL-able argument (here T can be names, value).
+  // T*          - NULL-able argument (here T can be names)
+  // value*      - NULL-able any type (never NULL itself, use value::null)
   // optional<T> - optional argument (here T can be T*, names, value)
   //
   // Optional arguments must be last. In case of a failure the function is
@@ -281,6 +282,15 @@ namespace build2
     }
   };
 
+  template <>
+  struct function_arg<value*>: function_arg<value>
+  {
+    static const bool null = true;
+
+    static value*
+    cast (value* v) {return v;} // NULL indicator in value::null.
+  };
+
   template <typename T>
   struct function_arg<optional<T>>: function_arg<T>
   {
diff --git a/build2/function.cxx b/build2/function.cxx
index 46dc403..e76f0c2 100644
--- a/build2/function.cxx
+++ b/build2/function.cxx
@@ -295,6 +295,7 @@ namespace build2
   //
   function_map functions;
 
+  void builtin_functions ();       // functions-builtin.cxx
   void path_functions ();          // functions-path.cxx
   void process_path_functions ();  // functions-process-path.cxx
 
@@ -302,6 +303,7 @@ namespace build2
   {
     functions_init ()
     {
+      builtin_functions ();
       path_functions ();
       process_path_functions ();
     }
diff --git a/build2/functions-builtin.cxx b/build2/functions-builtin.cxx
new file mode 100644
index 0000000..448bb53
--- /dev/null
+++ b/build2/functions-builtin.cxx
@@ -0,0 +1,24 @@
+// file      : build2/functions-builtin.cxx -*- C++ -*-
+// copyright : Copyright (c) 2014-2016 Code Synthesis Ltd
+// license   : MIT; see accompanying LICENSE file
+
+#include <build2/function>
+#include <build2/variable>
+
+using namespace std;
+
+namespace build2
+{
+  void
+  builtin_functions ()
+  {
+    function_family f ("builtin");
+
+    f["type"] = [](value* v) {return v->type != nullptr ? v->type->name : "";};
+
+    f["null"]  = [](value* v) {return v->null;};
+    f["empty"] = [](value v)  {return v.empty ();};
+
+    f["identity"] = [](value* v) {return move (*v);};
+  }
+}