tgba: simplify usage of named properties

* src/tgba/tgba.hh, src/tgba/tgba.cc (set_named_prop): Add a template
version.
(get_named_prop): Hide the old version, and supply a template version
that casts.
* src/bin/ltlcross.cc, src/hoaparse/hoaparse.yy, src/tgbaalgos/hoa.cc,
src/tgbaalgos/product.cc: Adjust usage.

src/bin/ltlcross.cc

@@ -1244,8 +1244,7 @@ namespace
 		state_set& s)
   {
     auto aut = m->get_aut();
-    auto ps = static_cast<const spot::product_states*>
-      (aut->get_named_prop("product-states"));
+    auto ps = aut->get_named_prop<const spot::product_states>("product-states");
     unsigned c = m->scc_count();
     for (unsigned n = 0; n < c; ++n)
       if (m->is_accepting_scc(n) || m->is_trivial(n))

src/hoaparse/hoaparse.yy

@@ -359,9 +359,7 @@ header-item: "States:" INT
 	     }
            | "name:" STRING
              {
-	       res.h->aut->set_named_prop("automaton-name", $2, [](void* name) {
-		   delete static_cast<std::string*>(name);
-		 });
+	       res.h->aut->set_named_prop("automaton-name", $2);
 	     }
            | "properties:" properties
            | HEADERNAME header-spec

src/tgba/tgba.cc

@@ -98,7 +98,7 @@ namespace spot
   }
 
   void*
-  tgba::get_named_prop(std::string s) const
+  tgba::get_named_prop_(std::string s) const
   {
     auto i = named_prop_.find(s);
     if (i == named_prop_.end())

src/tgba/tgba.hh

@@ -665,12 +665,28 @@ namespace spot
 		       std::pair<void*,
 				 std::function<void(void*)>>> named_prop_;
 #endif
+    void* get_named_prop_(std::string s) const;
+
   public:
 
 #ifndef SWIG
     void set_named_prop(std::string s,
 			void* val, std::function<void(void*)> destructor);
-    void* get_named_prop(std::string s) const;
+
+    template<typename T>
+    void set_named_prop(std::string s, T* val)
+    {
+      set_named_prop(s, val, [](void *p) { delete static_cast<T*>(p); });
+    }
+
+    template<typename T>
+    T* get_named_prop(std::string s) const
+    {
+      void* p = get_named_prop_(s);
+      if (!p)
+	return nullptr;
+      return static_cast<T*>(p);
+    }
 #endif
 
     bool has_single_acc_set() const

src/tgbaalgos/hoa.cc

@@ -250,9 +250,9 @@ namespace spot
 
     const char nl = newline ? '\n' : ' ';
     os << "HOA: v1" << nl;
-    auto* n = aut->get_named_prop("automaton-name");
+    auto n = aut->get_named_prop<std::string>("automaton-name");
     if (n)
-      escape_str(os << "name: \"", *static_cast<std::string*>(n)) << '"' << nl;
+      escape_str(os << "name: \"", *n) << '"' << nl;
     else if (f)
       escape_str(os << "name: \"", to_string(f)) << '"' << nl;
     os << "States: " << num_states << nl

src/tgbaalgos/product.cc

@@ -56,9 +56,7 @@ namespace spot
 				   + right->acc().num_sets());
 
     auto v = new product_states;
-    res->set_named_prop("product-states", v, [](void* vv) {
-	delete static_cast<product_states*>(vv);
-      });
+    res->set_named_prop("product-states", v);
 
     auto new_state =
       [&](unsigned left_state, unsigned right_state) -> unsigned