Add variable cast from lookup

18 files changed, 90 insertions, 70 deletions

diff --git a/build2/b.cxx b/build2/b.cxx
index f2cb9eb..b80fe5b 100644
--- a/build2/b.cxx
+++ b/build2/b.cxx
@@ -555,7 +555,7 @@ main (int argc, char* argv[])
           //
           if (auto l = rs.vars["subprojects"])
           {
-            for (const auto& p: cast<subprojects> (*l))
+            for (const auto& p: cast<subprojects> (l))
             {
               if (out_base.sub (out_root / p.second))
                 fail << tn << " is in a subproject of " << out_root <<
diff --git a/build2/bin/rule.cxx b/build2/bin/rule.cxx
index d74dd65..b5d5ca6 100644
--- a/build2/bin/rule.cxx
+++ b/build2/bin/rule.cxx
@@ -46,7 +46,7 @@ namespace build2
       // Get the library type to build. If not set for a target, this
       // should be configured at the project scope by init_lib().
       //
-      const string& type (cast<string> (*t["bin.lib"]));
+      const string& type (cast<string> (t["bin.lib"]));
 
       bool ar (type == "static" || type == "both");
       bool so (type == "shared" || type == "both");
@@ -121,7 +121,7 @@ namespace build2
       //   prerequisite vs prerequisite_target.
       //
       //
-      const string& type (cast<string> (*t["bin.lib"]));
+      const string& type (cast<string> (t["bin.lib"]));
       bool ar (type == "static" || type == "both");
       bool so (type == "shared" || type == "both");
 
diff --git a/build2/cli/module.cxx b/build2/cli/module.cxx
index 907bd0b..4e81908 100644
--- a/build2/cli/module.cxx
+++ b/build2/cli/module.cxx
@@ -45,7 +45,7 @@ namespace build2
       {
         auto l (base["cxx.loaded"]);
 
-        if (!l || !cast<bool> (*l))
+        if (!l || !cast<bool> (l))
           fail (loc) << "cxx module must be loaded before cli";
       }
 
@@ -90,7 +90,7 @@ namespace build2
       {
         auto l (root["config.cli.configured"]);
 
-        if (l && !cast<bool> (*l))
+        if (l && !cast<bool> (l))
           return false;
       }
 
diff --git a/build2/cli/rule.cxx b/build2/cli/rule.cxx
index 243c6aa..de14aa1 100644
--- a/build2/cli/rule.cxx
+++ b/build2/cli/rule.cxx
@@ -244,7 +244,7 @@ namespace build2
       path rels (relative (s->path ()));
 
       scope& rs (t.root_scope ());
-      const string& cli (cast<string> (*rs["config.cli"]));
+      const string& cli (cast<string> (rs["config.cli"]));
 
       cstrings args {cli.c_str ()};
 
diff --git a/build2/config/operation.cxx b/build2/config/operation.cxx
index 8047e61..245aed7 100644
--- a/build2/config/operation.cxx
+++ b/build2/config/operation.cxx
@@ -86,7 +86,7 @@ namespace build2
 
         if (auto l = root.vars["amalgamation"])
         {
-          const dir_path& d (cast<dir_path> (*l));
+          const dir_path& d (cast<dir_path> (l));
 
           ofs << "# Base configuration inherited from " << d << endl
               << "#" << endl;
@@ -188,7 +188,7 @@ namespace build2
       //
       if (auto l = root.vars["subprojects"])
       {
-        for (auto p: cast<subprojects> (*l))
+        for (auto p: cast<subprojects> (l))
         {
           const dir_path& pd (p.second);
           dir_path out_nroot (out_root / pd);
@@ -313,7 +313,7 @@ namespace build2
       //
       if (auto l = root.vars["subprojects"])
       {
-        for (auto p: cast<subprojects> (*l))
+        for (auto p: cast<subprojects> (l))
         {
           const dir_path& pd (p.second);
 
diff --git a/build2/cxx/compile.cxx b/build2/cxx/compile.cxx
index a2b00de..cf0c91c 100644
--- a/build2/cxx/compile.cxx
+++ b/build2/cxx/compile.cxx
@@ -130,7 +130,7 @@ namespace build2
       //
       if (a == perform_update_id)
       {
-        const string& sys (cast<string> (*rs["cxx.target.system"]));
+        const string& sys (cast<string> (rs["cxx.target.system"]));
 
         // The cached prerequisite target should be the same as what is in
         // t.prerequisite_targets since we used standard search() and match()
@@ -165,7 +165,7 @@ namespace build2
 
         // Then the compiler checksum.
         //
-        if (dd.expect (cast<string> (*rs["cxx.checksum"])) != nullptr)
+        if (dd.expect (cast<string> (rs["cxx.checksum"])) != nullptr)
           l4 ([&]{trace << "compiler mismatch forcing update of " << t;});
 
         // Then the options checksum.
@@ -237,7 +237,7 @@ namespace build2
         -> const target_type*
       {
         if (auto l = s.lookup (tt, n, var))
-          if (cast<string> (*l) == e)
+          if (cast<string> (l) == e)
             return &tt;
 
         return nullptr;
@@ -283,7 +283,7 @@ namespace build2
 
       if (auto l = t[var])
       {
-        const auto& v (cast<strings> (*l));
+        const auto& v (cast<strings> (l));
 
         for (auto i (v.begin ()), e (v.end ()); i != e; ++i)
         {
@@ -461,8 +461,8 @@ namespace build2
 
       auto init_args = [&t, &s, &rs, &args, &cxx_std] ()
       {
-        const string& cxx (cast<string> (*rs["config.cxx"]));
-        const string& sys (cast<string> (*rs["cxx.target.system"]));
+        const string& cxx (cast<string> (rs["config.cxx"]));
+        const string& sys (cast<string> (rs["cxx.target.system"]));
 
         args.push_back (cxx.c_str ());
 
@@ -923,8 +923,8 @@ namespace build2
       path rels (relative (s->path ()));
 
       scope& rs (t.root_scope ());
-      const string& cxx (cast<string> (*rs["config.cxx"]));
-      const string& sys (cast<string> (*rs["cxx.target.system"]));
+      const string& cxx (cast<string> (rs["config.cxx"]));
+      const string& sys (cast<string> (rs["cxx.target.system"]));
 
       cstrings args {cxx.c_str ()};
 
diff --git a/build2/cxx/link.cxx b/build2/cxx/link.cxx
index ea20a47..c0ea6d3 100644
--- a/build2/cxx/link.cxx
+++ b/build2/cxx/link.cxx
@@ -42,7 +42,7 @@ namespace build2
       case type::so: var = "bin.libso.lib"; break;
       }
 
-      const auto& v (cast<strings> (*t[var]));
+      const auto& v (cast<strings> (t[var]));
       return v[0] == "shared"
         ? v.size () > 1 && v[1] == "static" ? order::so_a : order::so
         : v.size () > 1 && v[1] == "shared" ? order::a_so : order::a;
@@ -52,7 +52,7 @@ namespace build2
     link_member (bin::lib& l, order lo)
     {
       bool lso (true);
-      const string& at (cast<string> (*l["bin.lib"])); // Available types.
+      const string& at (cast<string> (l["bin.lib"])); // Available types.
 
       switch (lo)
       {
@@ -92,7 +92,7 @@ namespace build2
       //
       if (auto l = bs["cxx.loptions"])
       {
-        const auto& v (cast<strings> (*l));
+        const auto& v (cast<strings> (l));
 
         for (auto i (v.begin ()), e (v.end ()); i != e; ++i)
         {
@@ -123,7 +123,7 @@ namespace build2
       cstrings args;
       string std_storage;
 
-      args.push_back (cast<string> (*rs["config.cxx"]).c_str ());
+      args.push_back (cast<string> (rs["config.cxx"]).c_str ());
       append_options (args, bs, "cxx.coptions");
       append_std (args, bs, std_storage);
       append_options (args, bs, "cxx.loptions");
@@ -218,7 +218,7 @@ namespace build2
         return p.target;
 
       scope& rs (*p.scope.root_scope ());
-      const string& sys (cast<string> (*rs["cxx.target.system"]));
+      const string& sys (cast<string> (rs["cxx.target.system"]));
 
       bool l (p.is_a<lib> ());
       const string* ext (l ? nullptr : p.ext); // Only for liba/libso.
@@ -483,7 +483,7 @@ namespace build2
       path_target& t (static_cast<path_target&> (xt));
 
       scope& rs (t.root_scope ());
-      const string& sys (cast<string> (*rs["cxx.target.system"]));
+      const string& sys (cast<string> (rs["cxx.target.system"]));
 
       type lt (link_type (t));
       bool so (lt == type::so);
@@ -510,7 +510,7 @@ namespace build2
         case type::so:
           {
             auto l (t["bin.libprefix"]);
-            const char* p (l ? cast<string> (*l).c_str () : "lib");
+            const char* p (l ? cast<string> (l).c_str () : "lib");
 
             const char* e;
             if (lt == type::a)
@@ -769,7 +769,7 @@ namespace build2
       bool up (execute_prerequisites (a, t, t.mtime ()));
 
       scope& rs (t.root_scope ());
-      const string& sys (cast<string> (*rs["cxx.target.system"]));
+      const string& sys (cast<string> (rs["cxx.target.system"]));
 
       // Check/update the dependency database.
       //
@@ -793,10 +793,10 @@ namespace build2
 
         const char* rl (
           ranlib
-          ? cast<string> (*rs["bin.ranlib.checksum"]).c_str ()
+          ? cast<string> (rs["bin.ranlib.checksum"]).c_str ()
           : "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855");
 
-        if (dd.expect (cast<string> (*rs["bin.ar.checksum"])) != nullptr)
+        if (dd.expect (cast<string> (rs["bin.ar.checksum"])) != nullptr)
           l4 ([&]{trace << "ar mismatch forcing update of " << t;});
 
         if (dd.expect (rl) != nullptr)
@@ -804,7 +804,7 @@ namespace build2
       }
       else
       {
-        if (dd.expect (cast<string> (*rs["cxx.checksum"])) != nullptr)
+        if (dd.expect (cast<string> (rs["cxx.checksum"])) != nullptr)
           l4 ([&]{trace << "compiler mismatch forcing update of " << t;});
       }
 
@@ -877,7 +877,7 @@ namespace build2
         // precedence.
         //
         if (auto l = t["bin.rpath"])
-          for (const string& p: cast<strings> (*l))
+          for (const string& p: cast<strings> (l))
             sargs.push_back ("-Wl,-rpath," + p);
 
         // Then the paths of the shared libraries we are linking to. Unless
@@ -978,12 +978,12 @@ namespace build2
 
       if (lt == type::a)
       {
-        args[0] = cast<string> (*rs["config.bin.ar"]).c_str ();
+        args[0] = cast<string> (rs["config.bin.ar"]).c_str ();
         args.push_back (relt.string ().c_str ());
       }
       else
       {
-        args[0] = cast<string> (*rs["config.cxx"]).c_str ();
+        args[0] = cast<string> (rs["config.cxx"]).c_str ();
         args.push_back ("-o");
         args.push_back (relt.string ().c_str ());
       }
@@ -1048,7 +1048,7 @@ namespace build2
       if (ranlib)
       {
         const char* args[] = {
-          cast<string> (*ranlib).c_str (), relt.string ().c_str (), nullptr};
+          cast<string> (ranlib).c_str (), relt.string ().c_str (), nullptr};
 
         if (verb >= 2)
           print_process (args);
diff --git a/build2/cxx/module.cxx b/build2/cxx/module.cxx
index d491079..18f9e53 100644
--- a/build2/cxx/module.cxx
+++ b/build2/cxx/module.cxx
@@ -46,7 +46,7 @@ namespace build2
       {
         auto l (b["bin.loaded"]);
 
-        if (!l || !cast<bool> (*l))
+        if (!l || !cast<bool> (l))
           load_module (false, "bin", r, b, loc);
       }
 
diff --git a/build2/cxx/utility.txx b/build2/cxx/utility.txx
index c20e437..4d38513 100644
--- a/build2/cxx/utility.txx
+++ b/build2/cxx/utility.txx
@@ -14,7 +14,7 @@ namespace build2
     {
       if (auto l = t["cxx.std"])
       {
-        const string& v (cast<string> (*l));
+        const string& v (cast<string> (l));
 
         // Translate 11 to 0x and 14 to 1y for compatibility with older
         // versions of the compiler.
diff --git a/build2/dist/operation.cxx b/build2/dist/operation.cxx
index 4489485..cb418be 100644
--- a/build2/dist/operation.cxx
+++ b/build2/dist/operation.cxx
@@ -90,7 +90,7 @@ namespace build2
         fail << "unknown root distribution directory" <<
           info << "did you forget to specify config.dist.root?";
 
-      const dir_path& dist_root (cast<dir_path> (*l));
+      const dir_path& dist_root (cast<dir_path> (l));
 
       if (!dir_exists (dist_root))
         fail << "root distribution directory " << dist_root
@@ -102,8 +102,8 @@ namespace build2
         fail << "unknown distribution package name" <<
           info << "did you forget to set dist.package?";
 
-      const string& dist_package (cast<string> (*l));
-      const string& dist_cmd (cast<string> (*rs->vars["dist.cmd"]));
+      const string& dist_package (cast<string> (l));
+      const string& dist_cmd (cast<string> (rs->vars["dist.cmd"]));
 
       // Get the list of operations supported by this project. Skip
       // default_id.
@@ -171,7 +171,7 @@ namespace build2
       //
       if (auto l = rs->vars["subprojects"])
       {
-        for (auto p: cast<subprojects> (*l))
+        for (auto p: cast<subprojects> (l))
         {
           const dir_path& pd (p.second);
           dir_path out_nroot (out_root / pd);
@@ -209,7 +209,7 @@ namespace build2
           //
           auto l ((*ft)[dist_var]);
 
-          if (l && !cast<bool> (*l))
+          if (l && !cast<bool> (l))
             l5 ([&]{trace << "excluding " << *ft;});
           else
             files.push_back (ft);
@@ -223,7 +223,7 @@ namespace build2
           //
           auto l ((*ft)[dist_var]);
 
-          if (l && cast<bool> (*l))
+          if (l && cast<bool> (l))
           {
             l5 ([&]{trace << "including " << *ft;});
             files.push_back (ft);
@@ -295,7 +295,7 @@ namespace build2
       //
       if (auto l = rs->vars["dist.archives"])
       {
-        for (const string& e: cast<strings> (*l))
+        for (const string& e: cast<strings> (l))
           archive (dist_root, dist_package, e);
       }
     }
diff --git a/build2/file.cxx b/build2/file.cxx
index 30ebed4..9097703 100644
--- a/build2/file.cxx
+++ b/build2/file.cxx
@@ -660,7 +660,7 @@ namespace build2
     if (!l)
       return;
 
-    const dir_path& d (cast<dir_path> (*l));
+    const dir_path& d (cast<dir_path> (l));
     dir_path out_root (root.out_path () / d);
     out_root.normalize ();
 
@@ -712,7 +712,7 @@ namespace build2
   {
     if (auto l = root.vars["subprojects"])
     {
-      for (const auto& p: cast<subprojects> (*l))
+      for (const auto& p: cast<subprojects> (l))
       {
         dir_path out_root (root.out_path () / p.second);
 
@@ -819,7 +819,7 @@ namespace build2
     {
       // First check the amalgamation itself.
       //
-      if (r != &iroot && cast<string> (*r->vars["project"]) == project)
+      if (r != &iroot && cast<string> (r->vars["project"]) == project)
       {
         out_root = r->out_path ();
         break;
@@ -827,7 +827,7 @@ namespace build2
 
       if (auto l = r->vars["subprojects"])
       {
-        const auto& m (cast<subprojects> (*l));
+        const auto& m (cast<subprojects> (l));
         auto i (m.find (project));
 
         if (i != m.end ())
@@ -851,7 +851,7 @@ namespace build2
 
       if (auto l = iroot[var])
       {
-        out_root = cast<dir_path> (*l);
+        out_root = cast<dir_path> (l);
 
         if (l.belongs (*global_scope)) // A value from command line.
         {
@@ -911,7 +911,7 @@ namespace build2
         //
         if (auto l = root->vars["src_root"])
         {
-          const dir_path& p (cast<dir_path> (*l));
+          const dir_path& p (cast<dir_path> (l));
 
           if (!src_root.empty () && p != src_root)
             fail (loc) << "bootstrapped src_root " << p << " does not match "
@@ -928,12 +928,12 @@ namespace build2
 
       // Now we know this project's name as well as all its subprojects.
       //
-      if (cast<string> (*root->vars["project"]) == project)
+      if (cast<string> (root->vars["project"]) == project)
         break;
 
       if (auto l = root->vars["subprojects"])
       {
-        const auto& m (cast<subprojects> (*l));
+        const auto& m (cast<subprojects> (l));
         auto i (m.find (project));
 
         if (i != m.end ())
diff --git a/build2/install/module.cxx b/build2/install/module.cxx
index 8e3d6fd..3890901 100644
--- a/build2/install/module.cxx
+++ b/build2/install/module.cxx
@@ -154,7 +154,7 @@ namespace build2
       if (first)
       {
         bool s (config::specified (r, "config.install"));
-        const string& n (cast<string> (*r["project"]));
+        const string& n (cast<string> (r["project"]));
 
         set_dir (s, r, "root",      "",      "", "755", "install");
         set_dir (s, r, "data_root", "root",  "644");
diff --git a/build2/install/rule.cxx b/build2/install/rule.cxx
index 89463f8..25259cf 100644
--- a/build2/install/rule.cxx
+++ b/build2/install/rule.cxx
@@ -31,7 +31,7 @@ namespace build2
       if (!l)
         return nullptr;
 
-      const dir_path& r (cast<dir_path> (*l));
+      const dir_path& r (cast<dir_path> (l));
       return r.simple () && r.string () == "false" ? nullptr : &r;
     }
 
@@ -64,7 +64,7 @@ namespace build2
         //
         auto l (pt["install"]);
 
-        if (l && cast<dir_path> (*l).string () == "false")
+        if (l && cast<dir_path> (l).string () == "false")
         {
           l5 ([&]{trace << "ignoring " << pt;});
           continue;
@@ -148,7 +148,7 @@ namespace build2
         // See if the user instructed us not to install it.
         //
         auto l ((*pt)["install"]);
-        if (l && cast<dir_path> (*l).string () == "false")
+        if (l && cast<dir_path> (l).string () == "false")
           continue;
 
         build2::match (a, *pt);
@@ -358,11 +358,11 @@ namespace build2
         //
         if (var != nullptr)
         {
-          if (auto l = s[*var + ".sudo"])     r.sudo = cast<string> (*l);
-          if (auto l = s[*var + ".cmd"])      r.cmd = cast<string> (*l);
-          if (auto l = s[*var + ".mode"])     r.mode = cast<string> (*l);
-          if (auto l = s[*var + ".dir_mode"]) r.dir_mode = cast<string> (*l);
-          if (auto l = s[*var + ".options"])  r.options = cast<strings> (*l);
+          if (auto l = s[*var + ".sudo"])     r.sudo = cast<string> (l);
+          if (auto l = s[*var + ".cmd"])      r.cmd = cast<string> (l);
+          if (auto l = s[*var + ".mode"])     r.mode = cast<string> (l);
+          if (auto l = s[*var + ".dir_mode"]) r.dir_mode = cast<string> (l);
+          if (auto l = s[*var + ".options"])  r.options = cast<strings> (l);
         }
 
         // Set defaults for unspecified components.
@@ -403,12 +403,12 @@ namespace build2
       //
       install_dir d (
         resolve (t.base_scope (),
-                 cast<dir_path> (*t["install"]))); // We know it's there.
+                 cast<dir_path> (t["install"]))); // We know it's there.
 
       // Override mode if one was specified.
       //
       if (auto l = t["install.mode"])
-        d.mode = cast<string> (*l);
+        d.mode = cast<string> (l);
 
       install (d, ft);
       return (r |= target_state::changed);
diff --git a/build2/target.txx b/build2/target.txx
index 2cb4d2e..b7d41f2 100644
--- a/build2/target.txx
+++ b/build2/target.txx
@@ -26,7 +26,7 @@ namespace build2
     {
       // Help the user here and strip leading '.' from the extension.
       //
-      const string& e (cast<string> (*l));
+      const string& e (cast<string> (l));
       return &extension_pool.find (
         !e.empty () && e.front () == '.' ? string (e, 1) : e);
     }
diff --git a/build2/test/rule.cxx b/build2/test/rule.cxx
index 0b3f59f..8c89bc7 100644
--- a/build2/test/rule.cxx
+++ b/build2/test/rule.cxx
@@ -70,7 +70,7 @@ namespace build2
           l = t.base_scope ()[
             var_pool.find<bool> (string("test.") + t.type ().name)];
 
-        r = l && cast<bool> (*l);
+        r = l && cast<bool> (l);
       }
 
       // If this is the update pre-operation, then all we really need to
@@ -181,12 +181,12 @@ namespace build2
           fail << "both test.roundtrip and test.input/output specified "
                << "for target " << t;
 
-        in = on = &cast<name> (*rl);
+        in = on = &cast<name> (rl);
       }
       else
       {
-        in = il ? &cast<name> (*il) : nullptr;
-        on = ol ? &cast<name> (*ol) : nullptr;
+        in = il ? &cast<name> (il) : nullptr;
+        on = ol ? &cast<name> (ol) : nullptr;
       }
 
       // Resolve them to targets, which normally would be existing files
@@ -296,7 +296,7 @@ namespace build2
       }
 
       if (l)
-        append_options (args, cast<strings> (*l));
+        append_options (args, cast<strings> (l));
     }
 
     // The format of args shall be:
diff --git a/build2/utility.cxx b/build2/utility.cxx
index 29e8b1e..71aed79 100644
--- a/build2/utility.cxx
+++ b/build2/utility.cxx
@@ -147,14 +147,14 @@ namespace build2
   append_options (cstrings& args, const lookup<const value>& l)
   {
     if (l)
-      append_options (args, cast<strings> (*l));
+      append_options (args, cast<strings> (l));
   }
 
   void
   hash_options (sha256& csum, const lookup<const value>& l)
   {
     if (l)
-      hash_options (csum, cast<strings> (*l));
+      hash_options (csum, cast<strings> (l));
   }
 
   void
@@ -181,7 +181,7 @@ namespace build2
   {
     if (l)
     {
-      for (const string& s: cast<strings> (*l))
+      for (const string& s: cast<strings> (l))
       {
         if (s == option)
           return true;
diff --git a/build2/variable b/build2/variable
index b5a32d8..57debfa 100644
--- a/build2/variable
+++ b/build2/variable
@@ -21,6 +21,7 @@ namespace build2
 {
   class value;
   struct variable;
+  template <typename> struct lookup;
 
   struct value_type
   {
@@ -185,15 +186,20 @@ namespace build2
   bool operator== (const value&, const value&);
   bool operator!= (const value&, const value&);
 
-  // Value cast.
+  // Value cast. The first three expect the value to be not NULL. The cast
+  // from lookup expects the value to aslo be defined.
   //
   // Why are these non-members? The cast is easier on the eyes and is also
   // consistent with the cast operators. The other two are for symmetry.
   //
+  //
   template <typename T> T& cast (value&);
   template <typename T> T&& cast (value&&);
   template <typename T> const T& cast (const value&);
 
+  template <typename T> T& cast (const lookup<value>&);
+  template <typename T> const T& cast (const lookup<const value>&);
+
   // Assign value type to the value. Variable is normally only used for
   // diagnostics.
   //
diff --git a/build2/variable.ixx b/build2/variable.ixx
index a129835..8a03996 100644
--- a/build2/variable.ixx
+++ b/build2/variable.ixx
@@ -104,6 +104,20 @@ namespace build2
   }
 
   template <typename T>
+  inline T&
+  cast (const lookup<value>& l)
+  {
+    return cast<T> (*l);
+  }
+
+  template <typename T>
+  inline const T&
+  cast (const lookup<const value>& l)
+  {
+    return cast<T> (*l);
+  }
+
+  template <typename T>
   inline void
   typify (value& v, const variable& var)
   {