106 lines
2.5 KiB
C++
106 lines
2.5 KiB
C++
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#pragma once
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#include <utility>
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#include <cassert>
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// The difference between Opt and Box is that Opt can be initialized or
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// assigned to nullptr, while Box can only be null after being moved.
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// Besides, the data in const Opt can still be modified, while the data
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// in const Box cannot be modified.
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// Both Opt and Box can be copied and moved. The data in them will also
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// be copied when they are copied.
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template <typename T>
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class Opt {
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T *data;
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Opt(T *data):
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data(data) {}
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public:
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Opt(std::nullptr_t):
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data(nullptr) {}
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Opt(Opt const &other):
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data(other.data ? new T(*other.data) : nullptr) {}
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Opt(Opt &&other):
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data(other.data) {
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other.data = nullptr;
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}
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Opt &operator=(std::nullptr_t) {
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delete data;
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data = nullptr;
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return *this;
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}
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Opt &operator=(Opt const &other) {
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if (this != &other) {
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delete data;
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data = other.data ? new T(*other.data) : nullptr;
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}
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return *this;
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}
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Opt &operator=(Opt &&other) {
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assert(this != &other); // self-assignment is not allowed
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delete data;
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data = other.data;
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other.data = nullptr;
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return *this;
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}
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~Opt() {
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delete data;
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}
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template <typename... Args>
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static Opt make(Args &&...args) {
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return Opt(new T(std::forward<Args>(args)...));
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}
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T &operator*() const & {
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return *data;
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}
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T *operator->() const & {
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return data;
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}
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operator bool() const {
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return data;
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}
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};
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template <typename T>
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class Box {
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T *data;
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Box(T *data):
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data(data) {}
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public:
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Box(Box const &other):
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data(new T(*other.data)) {}
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Box(Box &&other):
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data(other.data) {
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other.data = nullptr;
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}
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Box &operator=(Box const &other) {
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if (this != &other) {
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delete data;
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data = new T(*other.data);
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}
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return *this;
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}
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Box &operator=(Box &&other) {
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assert(this != &other); // self-assignment is not allowed
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delete data;
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data = other.data;
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other.data = nullptr;
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return *this;
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}
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~Box() {
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delete data;
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}
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template <typename... Args>
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static Box make(Args &&...args) {
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return Box(new T(std::forward<Args>(args)...));
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}
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T const &operator*() const & {
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return *data;
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}
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T const *operator->() const & {
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return data;
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}
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T &operator*() & {
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return *data;
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}
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T *operator->() & {
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return data;
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}
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};
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