Allow clearing of state storage.

alialib · Sep 9, 2020 · e30b654 · e30b654
1 parent a1f784c
commit e30b654
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Showing 2 changed files with 56 additions and 10 deletions.
diff --git a/src/alia/signals/state.hpp b/src/alia/signals/state.hpp
@@ -26,7 +26,7 @@ struct state_storage
     bool
     is_initialized() const
     {
-        return version_ != 0;
+        return (version_ & 1) != 0;
     }
 
     Value const&
@@ -45,7 +45,15 @@ struct state_storage
     set(Value value)
     {
         value_ = std::move(value);
-        handle_change();
+        set_valid_flag();
+        handle_tracked_change();
+    }
+
+    void
+    clear()
+    {
+        clear_valid_flag();
+        handle_tracked_change();
     }
 
     // If you REALLY need direct, non-const access to the underlying state,
@@ -64,7 +72,8 @@ struct state_storage
     Value&
     nonconst_ref()
     {
-        handle_change();
+        set_valid_flag();
+        handle_tracked_change();
         return value_;
     }
 
@@ -74,10 +83,19 @@ struct state_storage
     Value&
     untracked_nonconst_ref()
     {
-        ++version_;
+        set_valid_flag();
+        inc_version();
         return value_;
     }
 
+    // Similarly unsafe way to clear the value.
+    void
+    untracked_clear()
+    {
+        clear_valid_flag();
+        inc_version();
+    }
+
     // Update the container that the state is part of.
     void
     refresh_container(component_container_ptr const& container)
@@ -87,15 +105,33 @@ struct state_storage
 
  private:
     void
-    handle_change()
+    set_valid_flag()
+    {
+        version_ |= 1;
+    }
+
+    void
+    clear_valid_flag()
+    {
+        version_ &= ~1;
+    }
+
+    void
+    inc_version()
+    {
+        version_ += 2;
+    }
+
+    void
+    handle_tracked_change()
     {
-        ++version_;
+        inc_version();
         mark_dirty_component(container_);
     }
 
     Value value_;
-    // version_ is incremented for each change in the value of the state.
-    // If this is 0, the state is considered uninitialized.
+    // version_ is incremented for each change in the value (or validity) of
+    // the state. The lowest bit of this indicates if the value is valid.
     unsigned version_;
     component_container_ptr container_;
 };

diff --git a/unit_tests/signals/state.cpp b/unit_tests/signals/state.cpp
@@ -14,14 +14,24 @@ TEST_CASE("state_storage", "[signals][state]")
     state_storage<int> s;
     REQUIRE(!s.is_initialized());
     REQUIRE(s.version() == 0);
+    unsigned version = 0;
+
     s.set(1);
     REQUIRE(s.is_initialized());
-    REQUIRE(s.version() == 1);
+    REQUIRE(s.version() != 0);
+    version = s.version();
     REQUIRE(s.get() == 1);
+
     s.nonconst_ref() = 4;
     REQUIRE(s.is_initialized());
-    REQUIRE(s.version() == 2);
+    REQUIRE(s.version() != version);
+    version = s.version();
     REQUIRE(s.get() == 4);
+
+    s.clear();
+    REQUIRE(!s.is_initialized());
+    REQUIRE(s.version() != version);
+    version = s.version();
 }
 
 TEST_CASE("basic get_state", "[signals][state]")