diff --git a/src/coders/GLSLExtension.cpp b/src/coders/GLSLExtension.cpp
index f3f2e29a..1e25c934 100644
--- a/src/coders/GLSLExtension.cpp
+++ b/src/coders/GLSLExtension.cpp
@@ -42,10 +42,10 @@ const std::string& GLSLExtension::getHeader(const std::string& name) const {
     return found->second;
 }
 
-const std::string GLSLExtension::getDefine(const std::string& name) const {
+const std::string& GLSLExtension::getDefine(const std::string& name) const {
     auto found = defines.find(name);
     if (found == defines.end()) {
-        return "";
+        throw std::runtime_error("name '"+name+"' is not defined");
     }
     return found->second;
 }
@@ -84,7 +84,7 @@ inline void source_line(std::stringstream& ss, uint linenum) {
     ss << "#line " << linenum << "\n";
 }
 
-const std::string GLSLExtension::process(const fs::path& file, const std::string& source) {
+std::string GLSLExtension::process(const fs::path& file, const std::string& source) {
     std::stringstream ss;
     size_t pos = 0;
     uint linenum = 1;
diff --git a/src/coders/GLSLExtension.hpp b/src/coders/GLSLExtension.hpp
index 077c59ea..98884c28 100644
--- a/src/coders/GLSLExtension.hpp
+++ b/src/coders/GLSLExtension.hpp
@@ -24,12 +24,12 @@ public:
     void addHeader(const std::string& name, std::string source);
 
     const std::string& getHeader(const std::string& name) const;
-    const std::string getDefine(const std::string& name) const;
+    const std::string& getDefine(const std::string& name) const;
 
     bool hasHeader(const std::string& name) const;
     bool hasDefine(const std::string& name) const;
 
-    const std::string process(
+    std::string process(
         const std::filesystem::path& file, 
         const std::string& source
     );
diff --git a/src/coders/xml.cpp b/src/coders/xml.cpp
index e2d9925c..51c3046b 100644
--- a/src/coders/xml.cpp
+++ b/src/coders/xml.cpp
@@ -120,7 +120,7 @@ const std::string& Node::getTag() const {
     return tag;
 }
 
-const xmlattribute Node::attr(const std::string& name) const {
+const xmlattribute& Node::attr(const std::string& name) const {
     auto found = attrs.find(name);
     if (found == attrs.end()) {
         throw std::runtime_error("element <"+tag+" ...> missing attribute "+name);
@@ -128,7 +128,7 @@ const xmlattribute Node::attr(const std::string& name) const {
     return found->second;
 }
 
-const xmlattribute Node::attr(const std::string& name, const std::string& def) const {
+xmlattribute Node::attr(const std::string& name, const std::string& def) const {
     auto found = attrs.find(name);
     if (found == attrs.end()) {
         return Attribute(name, def);
diff --git a/src/coders/xml.hpp b/src/coders/xml.hpp
index 92004f54..c70ce9c2 100644
--- a/src/coders/xml.hpp
+++ b/src/coders/xml.hpp
@@ -68,14 +68,14 @@ namespace xml {
         /// @param name attribute name
         /// @throws std::runtime_error if element has no attribute 
         /// @return xmlattribute - {name, value}
-        const xmlattribute attr(const std::string& name) const;
+        const xmlattribute& attr(const std::string& name) const;
         
         /// @brief Get attribute by name
         /// @param name attribute name
         /// @param def default value will be returned wrapped in xmlattribute
         /// if element has no attribute 
         /// @return xmlattribute - {name, value} or {name, def} if not found*/
-        const xmlattribute attr(const std::string& name, const std::string& def) const;
+        xmlattribute attr(const std::string& name, const std::string& def) const;
 
         /// @brief Check if element has attribute
         /// @param name attribute name
diff --git a/src/frontend/UiDocument.cpp b/src/frontend/UiDocument.cpp
index face749f..3951e4e9 100644
--- a/src/frontend/UiDocument.cpp
+++ b/src/frontend/UiDocument.cpp
@@ -33,11 +33,11 @@ const std::string& UiDocument::getId() const {
     return id;
 }
 
-const std::shared_ptr<gui::UINode> UiDocument::getRoot() const {
+std::shared_ptr<gui::UINode> UiDocument::getRoot() const {
     return root;
 }
 
-const std::shared_ptr<gui::UINode> UiDocument::get(const std::string& id) const {
+std::shared_ptr<gui::UINode> UiDocument::get(const std::string& id) const {
     auto found = map.find(id);
     if (found == map.end()) {
         return nullptr;
diff --git a/src/frontend/UiDocument.hpp b/src/frontend/UiDocument.hpp
index c571449d..504411a9 100644
--- a/src/frontend/UiDocument.hpp
+++ b/src/frontend/UiDocument.hpp
@@ -41,8 +41,8 @@ public:
     const std::string& getId() const;
     const uinodes_map& getMap() const;
     uinodes_map& getMapWriteable();
-    const std::shared_ptr<gui::UINode> getRoot() const;
-    const std::shared_ptr<gui::UINode> get(const std::string& id) const;
+    std::shared_ptr<gui::UINode> getRoot() const;
+    std::shared_ptr<gui::UINode> get(const std::string& id) const;
     const uidocscript& getScript() const;
     scriptenv getEnvironment() const;
 
diff --git a/src/graphics/ui/elements/InventoryView.cpp b/src/graphics/ui/elements/InventoryView.cpp
index d05f028d..b364425f 100644
--- a/src/graphics/ui/elements/InventoryView.cpp
+++ b/src/graphics/ui/elements/InventoryView.cpp
@@ -114,8 +114,21 @@ SlotView::SlotView(
 }
 
 void SlotView::draw(const DrawContext* pctx, Assets* assets) {
-    if (bound == nullptr)
+    if (bound == nullptr) {
         return;
+    }
+    itemid_t itemid = bound->getItemId();
+    if (itemid != prevItem) {
+        if (itemid) {
+            auto def = content->getIndices()->getItemDef(itemid);
+            tooltip = util::pascal_case(
+                langs::get(util::str2wstr_utf8(def->caption))
+            );
+        } else {
+            tooltip = L"";
+        }
+    }
+    prevItem = itemid;
 
     const int slotSize = InventoryView::SLOT_SIZE;
 
@@ -274,15 +287,12 @@ void SlotView::onFocus(gui::GUI* gui) {
     clicked(gui, mousecode::BUTTON_1);
 }
 
-const std::wstring SlotView::getTooltip() const {
-    const auto str = UINode::getTooltip();
-    if (!str.empty() || bound->isEmpty()) {
+const std::wstring& SlotView::getTooltip() const {
+    const auto& str = UINode::getTooltip();
+    if (!str.empty() || tooltip.empty()) {
         return str;
     }
-    auto def = content->getIndices()->getItemDef(bound->getItemId());
-    return util::pascal_case(
-        langs::get(util::str2wstr_utf8(def->caption))
-    ); // TODO: cache
+    return tooltip;
 }
 
 void SlotView::bind(
diff --git a/src/graphics/ui/elements/InventoryView.hpp b/src/graphics/ui/elements/InventoryView.hpp
index f5762d34..476b4d99 100644
--- a/src/graphics/ui/elements/InventoryView.hpp
+++ b/src/graphics/ui/elements/InventoryView.hpp
@@ -53,6 +53,9 @@ namespace gui {
 
         int64_t inventoryid = 0;
         ItemStack* bound = nullptr;
+
+        std::wstring tooltip;
+        itemid_t prevItem = 0;
     public:
         SlotView(SlotLayout layout);
 
@@ -63,7 +66,7 @@ namespace gui {
 
         virtual void clicked(gui::GUI*, mousecode) override;
         virtual void onFocus(gui::GUI*) override;
-        virtual const std::wstring getTooltip() const override;
+        virtual const std::wstring& getTooltip() const override;
 
         void bind(
             int64_t inventoryid,
diff --git a/src/graphics/ui/elements/UINode.cpp b/src/graphics/ui/elements/UINode.cpp
index 113161cf..b2c96721 100644
--- a/src/graphics/ui/elements/UINode.cpp
+++ b/src/graphics/ui/elements/UINode.cpp
@@ -138,7 +138,7 @@ void UINode::setTooltip(const std::wstring& text) {
     this->tooltip = text;
 }
 
-const std::wstring UINode::getTooltip() const {
+const std::wstring& UINode::getTooltip() const {
     return tooltip;
 }
 
diff --git a/src/graphics/ui/elements/UINode.hpp b/src/graphics/ui/elements/UINode.hpp
index c29a4461..056b933f 100644
--- a/src/graphics/ui/elements/UINode.hpp
+++ b/src/graphics/ui/elements/UINode.hpp
@@ -202,7 +202,7 @@ namespace gui {
         virtual bool isResizing() const;
 
         virtual void setTooltip(const std::wstring& text);
-        virtual const std::wstring getTooltip() const;
+        virtual const std::wstring& getTooltip() const;
 
         virtual void setTooltipDelay(float delay);
         virtual float getTooltipDelay() const;
diff --git a/src/logic/CommandsInterpreter.hpp b/src/logic/CommandsInterpreter.hpp
index 60cdce97..7d7d8508 100644
--- a/src/logic/CommandsInterpreter.hpp
+++ b/src/logic/CommandsInterpreter.hpp
@@ -120,7 +120,7 @@ namespace cmd {
         );
         Command* get(const std::string& name);
 
-        const std::unordered_map<std::string, Command> getCommands() const {
+        const std::unordered_map<std::string, Command>& getCommands() const {
             return commands;
         }
     };
diff --git a/src/logic/scripting/lua/LuaState.cpp b/src/logic/scripting/lua/LuaState.cpp
index 49f83439..524e3049 100644
--- a/src/logic/scripting/lua/LuaState.cpp
+++ b/src/logic/scripting/lua/LuaState.cpp
@@ -68,7 +68,7 @@ LuaState::LuaState() {
     setglobal(LAMBDAS_TABLE);
 }
 
-const std::string LuaState::envName(int env) {
+std::string LuaState::envName(int env) {
     return "_ENV"+util::mangleid(env);
 }
 
diff --git a/src/logic/scripting/lua/LuaState.hpp b/src/logic/scripting/lua/LuaState.hpp
index 58c538bd..74c0257d 100644
--- a/src/logic/scripting/lua/LuaState.hpp
+++ b/src/logic/scripting/lua/LuaState.hpp
@@ -29,7 +29,7 @@ namespace lua {
         LuaState();
         ~LuaState();
 
-        static const std::string envName(int env);
+        static std::string envName(int env);
         void loadbuffer(int env, const std::string& src, const std::string& file);
         int gettop() const;
         int pushivec3(lua_Integer x, lua_Integer y, lua_Integer z);
diff --git a/src/window/input.hpp b/src/window/input.hpp
index 50e26446..7c966087 100644
--- a/src/window/input.hpp
+++ b/src/window/input.hpp
@@ -157,7 +157,7 @@ struct Binding {
     void reset(keycode);
     void reset(mousecode);
 
-    inline const std::string text() const {
+    inline std::string text() const {
         switch (type) {
         case inputtype::keyboard: {
             return input_util::to_string(static_cast<keycode>(code));