avoid forcing conversions because of an issue with VS2019 (close #257)

src/entt/entity/registry.hpp

@@ -270,7 +270,7 @@ class basic_registry {
             pdata->pool = std::make_unique<pool_type<Component>>();
             pdata->remove.template connect<&pool_type<Component>::remove>(static_cast<pool_type<Component> *>(pdata->pool.get()));
 
-            pdata->clone = +[](const sparse_set<Entity> &other) -> std::unique_ptr<sparse_set<Entity>> {
+            pdata->clone = [](const sparse_set<Entity> &other) -> std::unique_ptr<sparse_set<Entity>> {
                 if constexpr(std::is_copy_constructible_v<std::decay_t<Component>>) {
                     return std::make_unique<pool_type<Component>>(static_cast<const pool_type<Component> &>(other));
                 } else {
@@ -1321,8 +1321,8 @@ public:
         if(!curr) {
             groups.push_back(group_data{
                 { sizeof...(Owned), sizeof...(Get), sizeof...(Exclude) },
-                decltype(group_data::group){new handler_type{}, +[](void *gptr) { delete static_cast<handler_type *>(gptr); }},
-                +[](const ENTT_ID_TYPE *other) {
+                decltype(group_data::group){new handler_type{}, [](void *gptr) { delete static_cast<handler_type *>(gptr); }},
+                [](const ENTT_ID_TYPE *other) {
                     const std::size_t ctypes[] = { type<Owned>()..., type<Get>()..., type<Exclude>()... };
                     return std::equal(std::begin(ctypes), std::end(ctypes), other);
                 }
@@ -1580,7 +1580,7 @@ public:
 
         if(it == vars.cend()) {
             vars.push_back({
-                decltype(ctx_variable::value){new Type{std::forward<Args>(args)...}, +[](void *ptr) { delete static_cast<Type *>(ptr); }},
+                decltype(ctx_variable::value){new Type{std::forward<Args>(args)...}, [](void *ptr) { delete static_cast<Type *>(ptr); }},
                 ctype
             });
 

src/entt/signal/delegate.hpp

@@ -107,7 +107,7 @@ class delegate<Ret(Args...)> {
     void connect(std::index_sequence<Index...>) ENTT_NOEXCEPT {
         data = nullptr;
 
-        fn = +[](const void *, std::tuple<Args...> args) -> Ret {
+        fn = [](const void *, std::tuple<Args...> args) -> Ret {
             static_assert(std::is_invocable_r_v<Ret, decltype(Function), std::tuple_element_t<Index, std::tuple<Args...>>...>);
             // Ret(...) allows void(...) to eat return values and avoid errors
             return Ret(std::invoke(Function, std::get<Index>(args)...));
@@ -118,7 +118,7 @@ class delegate<Ret(Args...)> {
     void connect(Type *value_or_instance, std::index_sequence<Index...>) ENTT_NOEXCEPT {
         data = value_or_instance;
 
-        fn = +[](const void *payload, std::tuple<Args...> args) -> Ret {
+        fn = [](const void *payload, std::tuple<Args...> args) -> Ret {
             Type *curr = nullptr;
 
             if constexpr(std::is_const_v<Type>) {