Inheritance is the base class of evil (Sean Parent)

最新推荐文章于 2022-12-28 14:31:44 发布

原创最新推荐文章于 2022-12-28 14:31:44 发布 · 1.2k 阅读

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本文介绍了一个使用模板元编程实现的对象绘制系统，并通过具体的代码示例展示了如何创建通用的数据结构来表示不同类型的对象。此外，还实现了简单的版本控制系统，包括提交(commit)和撤销(undo)操作，用于记录和回退文档历史。

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#include <iostream>
#include <vector>
#include <string>
#include <memory>
#include <cassert>

using namespace std;

template<typename T>
void draw(const T& x, ostream& out, size_t pos) {
out << string(pos, ' ') << x << "\n";
}

class object_t {
public:
template<typename T>
object_t(T x) : self_(make_shared<model<T>>(move(x))) {
cout << "ctor\n";
}

friend void draw(const object_t& x, ostream& out, size_t pos) {
x.self_->draw_(out, pos);
}

private:
struct concept_t {
virtual ~concept_t() = default;
virtual void draw_(ostream&, size_t) const = 0;
};

template<typename T>
struct model: concept_t {
model(T x) : data_(move(x)) {
}

void draw_(ostream& out, size_t pos) const {
draw(data_, out, pos);
}

T data_;
};

private:
shared_ptr<const concept_t> self_;
};

using document_t = vector<object_t>;

class my_class_t {
};

void draw(const my_class_t&, ostream& out, size_t pos) {
out << string(pos, ' ') << "my_class_t\n";

}

void draw(const document_t& x, ostream& out, size_t pos) {
out << string(pos, ' ') << "<document>\n";
for (const auto& e: x) {
draw(e, out, pos + 2);
}
out << string(pos, ' ') << "</document>\n";
}

using history_t = vector<document_t>;
void commit(history_t& x) {
assert(!x.empty());
x.push_back(x.back());
}

void undo(history_t& x) {
assert(!x.empty());
x.pop_back();
}

document_t& current(history_t& x) {
assert(!x.empty());
return x.back();
}

int main() {
history_t h(1);
current(h).emplace_back(0);
current(h).emplace_back(string("hello"));
draw(current(h), cout, 0);
cout << "-----------------------\n";

commit(h);

current(h).emplace_back(current(h));
current(h).emplace_back(my_class_t());
cout << "change hello\n";
current(h)[1] = string("world");

draw(current(h), cout, 0);
cout << "-----------------------\n";

undo(h);

draw(current(h), cout, 0);

return 0;
}