From 61617d7bb990f04970c6357d8e9a9095174d8fc4 Mon Sep 17 00:00:00 2001
From: Boris Kolpackov <boris@codesynthesis.com>
Date: Sun, 26 Jun 2016 16:36:53 +0200
Subject: Minor module interface cleanups

---
 build2/cli/module.cxx | 17 ++++++-----------
 build2/cxx/module.cxx | 12 ++++--------
 build2/file.cxx       |  2 +-
 build2/module         |  6 +++---
 build2/module.cxx     |  6 +++---
 build2/parser.cxx     |  2 +-
 build2/variable       |  7 +++++++
 build2/variable.ixx   |  8 ++++++++
 8 files changed, 33 insertions(+), 27 deletions(-)

diff --git a/build2/cli/module.cxx b/build2/cli/module.cxx
index 44b36a1..478c8a8 100644
--- a/build2/cli/module.cxx
+++ b/build2/cli/module.cxx
@@ -36,18 +36,13 @@ namespace build2
       tracer trace ("cli::init");
       l5 ([&]{trace << "for " << base.out_path ();});
 
-      // Make sure the cxx module has been loaded since we need its
-      // targets types (?xx{}). Note that we don't try to load it
-      // ourselves because of the non-trivial variable merging
-      // semantics. So it is better to let the user load cxx
-      // explicitly.
+      // Make sure the cxx module has been loaded since we need its targets
+      // types (?xx{}). Note that we don't try to load it ourselves because of
+      // the non-trivial variable merging semantics. So it is better to let
+      // the user load cxx explicitly.
       //
-      {
-        auto l (base["cxx.loaded"]);
-
-        if (!l || !cast<bool> (l))
-          fail (loc) << "cxx module must be loaded before cli";
-      }
+      if (!cast_false<bool> (base["cxx.loaded"]))
+        fail (loc) << "cxx module must be loaded before cli";
 
       // Enter module variables.
       //
diff --git a/build2/cxx/module.cxx b/build2/cxx/module.cxx
index b4ce142..c03763f 100644
--- a/build2/cxx/module.cxx
+++ b/build2/cxx/module.cxx
@@ -40,15 +40,11 @@ namespace build2
       tracer trace ("cxx::init");
       l5 ([&]{trace << "for " << b.out_path ();});
 
-      // Initialize the bin module. Only do this if it hasn't already
-      // been loaded so that we don't overwrite user's bin.* settings.
+      // Initialize the bin module. Only do this if it hasn't already been
+      // loaded so that we don't overwrite user's bin.* settings.
       //
-      {
-        auto l (b["bin.loaded"]);
-
-        if (!l || !cast<bool> (l))
-          load_module (false, "bin", r, b, loc);
-      }
+      if (!cast_false<bool> (b["bin.loaded"]))
+        load_module ("bin", r, b, loc);
 
       // Enter module variables.
       //
diff --git a/build2/file.cxx b/build2/file.cxx
index f5ce91c..8b6291a 100644
--- a/build2/file.cxx
+++ b/build2/file.cxx
@@ -781,7 +781,7 @@ namespace build2
 
       if (s.boot)
       {
-        load_module (false, n, root, root, s.loc);
+        load_module (n, root, root, s.loc);
         assert (!s.boot);
       }
     }
diff --git a/build2/module b/build2/module
index 25574d1..dcfe5d0 100644
--- a/build2/module
+++ b/build2/module
@@ -76,11 +76,11 @@ namespace build2
   // (false can only be returned if optional).
   //
   bool
-  load_module (bool optional,
-               const string& name,
+  load_module (const string& name,
                scope& root,
                scope& base,
-               const location&);
+               const location&,
+               bool optional = false);
 
   // Builtin modules.
   //
diff --git a/build2/module.cxx b/build2/module.cxx
index cfab057..1334689 100644
--- a/build2/module.cxx
+++ b/build2/module.cxx
@@ -50,11 +50,11 @@ namespace build2
   }
 
   bool
-  load_module (bool opt,
-               const string& name,
+  load_module (const string& name,
                scope& rs,
                scope& bs,
-               const location& loc)
+               const location& loc,
+               bool opt)
   {
     // First see if this modules has already been loaded for this project.
     //
diff --git a/build2/parser.cxx b/build2/parser.cxx
index 20cb75f..1edc7ba 100644
--- a/build2/parser.cxx
+++ b/build2/parser.cxx
@@ -1102,7 +1102,7 @@ namespace build2
         if (boot_)
           boot_module (n, *root_, l);
         else
-          load_module (optional, n, *root_, *scope_, l);
+          load_module (n, *root_, *scope_, l, optional);
       }
     }
 
diff --git a/build2/variable b/build2/variable
index a5f2ea5..c506a3e 100644
--- a/build2/variable
+++ b/build2/variable
@@ -252,6 +252,13 @@ namespace build2
   template <typename T> const T* cast_null (const value&);
   template <typename T> const T* cast_null (const lookup&);
 
+  // As above but returns false if the value is NULL (or not defined, in case
+  // of lookup). Note that the template argument is only for documentation and
+  // should be bool (or semantically compatible).
+  //
+  template <typename T> T cast_false (const value& v);
+  template <typename T> T cast_false (const lookup& l);
+
   // Assign value type to the value. In the second version the variable is
   // optional and is only used for diagnostics.
   //
diff --git a/build2/variable.ixx b/build2/variable.ixx
index e01e3d6..da86c39 100644
--- a/build2/variable.ixx
+++ b/build2/variable.ixx
@@ -158,6 +158,14 @@ namespace build2
   }
 
   template <typename T>
+  inline T
+  cast_false (const value& v) {return v && cast<T> (v);}
+
+  template <typename T>
+  inline T
+  cast_false (const lookup& l) {return l && cast<T> (l);}
+
+  template <typename T>
   inline void
   typify (value& v, const variable& var)
   {
-- 
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