tqchen commented on a change in pull request #5314: [RUNTIME][IR] Allow
non-nullable ObjectRef, introduce Optional<T>.
URL: https://github.com/apache/incubator-tvm/pull/5314#discussion_r407462403
##########
File path: include/tvm/runtime/container.h
##########
@@ -610,7 +611,146 @@ struct PackedFuncValueConverter<::tvm::runtime::String> {
}
};
+/*!
+ * \brief Optional container that to represent to a Nullable variant of T.
+ * \tparam T The original ObjectRef.
+ *
+ * \code
+ *
+ * Optional<String> opt0 = nullptr;
+ * Optional<String> opt1 = String("xyz");
+ * CHECK(opt0 == nullptr);
+ * CHECK(opt1 == "xyz");
+ *
+ * \endcode
+ */
+template<typename T>
+class Optional : public ObjectRef {
+ public:
+ using ContainerType = typename T::ContainerType;
+ static_assert(std::is_base_of<ObjectRef, T>::value,
+ "Optional is only defined for ObjectRef.");
+ // default constructors.
+ Optional() = default;
+ Optional(const Optional<T>&) = default;
+ Optional(Optional<T>&&) = default;
+ Optional<T>& operator=(const Optional<T>&) = default;
+ Optional<T>& operator=(Optional<T>&&) = default;
+ /*!
+ * \brief Construct from an ObjectPtr
+ * whose type already matches the ContainerType.
+ * \param ptr
+ */
+ explicit Optional(ObjectPtr<Object> ptr) : ObjectRef(ptr) {}
+ // nullptr handling.
+ // disallow implicit conversion as 0 can be implicitly converted to nullptr_t
+ explicit Optional(std::nullptr_t) {}
+ Optional<T>& operator=(std::nullptr_t) {
+ data_ = nullptr;
+ return *this;
+ }
+ // normal value handling.
+ Optional(T other) // NOLINT(*)
+ : ObjectRef(std::move(other)) {
+ }
+ Optional<T>& operator=(T other) {
+ ObjectRef::operator=(std::move(other));
+ return *this;
+ }
+ // delete the int constructor
+ // since Optional<Integer>(0) is ambiguious
+ // 0 can be implicitly casted to nullptr_t
+ explicit Optional(int val) = delete;
+ Optional<T>& operator=(int val) = delete;
+ /*!
+ * \return A not-null container value in the optional.
+ * \note This function performs not-null checking.
+ */
+ T value() const {
+ CHECK(data_ != nullptr);
+ return T(data_);
+ }
+ /*!
+ * \return The contained value if the Optional is not null
+ * otherwise return the default_value.
+ */
+ T value_or(T default_value) const {
+ return data_ != nullptr ? T(data_) : default_value;
+ }
+ /*! \return Whether the container is not nullptr.*/
+ explicit operator bool() const {
Review comment:
This overload is needed to enable sugar
```c++
if (auto opt = GetSomeOptional) {
// code
}
```
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