Make optional copyable when possible.

GitOrigin-RevId: 28c37171a9db3e868a21bc028ba24fee05833b35

tdutils/td/utils/optional.h

@@ -13,7 +13,7 @@
 
 namespace td {
 
-template <class T>
+template <class T, bool = std::is_copy_constructible<T>::value>
 class optional {
  public:
   optional() = default;
@@ -22,6 +22,25 @@ class optional {
                              int> = 0>
   optional(T1 &&t) : impl_(std::forward<T1>(t)) {
   }
+
+  optional(const optional &other) {
+    if (other) {
+      impl_ = Result<T>(other.value());
+    }
+  }
+
+  optional &operator=(const optional &other) {
+    if (other) {
+      impl_ = Result<T>(other.value());
+    } else {
+      impl_ = Result<T>();
+    }
+  }
+
+  optional(optional &&other) = default;
+  optional &operator=(optional &&other) = default;
+  ~optional() = default;
+
   explicit operator bool() const {
     return impl_.is_ok();
   }
@@ -39,4 +58,17 @@ class optional {
   Result<T> impl_;
 };
 
+template <typename T>
+struct optional<T, false> : optional<T, true> {
+  optional() = default;
+
+  using optional<T, true>::optional;
+
+  optional(const optional &other) = delete;
+  optional &operator=(const optional &other) = delete;
+  optional(optional &&) = default;
+  optional &operator=(optional &&) = default;
+  ~optional() = default;
+};
+
 }  // namespace td