Implement few builtin functions that can operate on any value

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

1 files changed, 11 insertions, 1 deletions

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>
   {