我有一些代码:
class Base {
virtual bool acceptsData(char*) = 0;
};
class Derived1 : public Base {
virtual bool acceptsData(char*) { /* do something */ }
};
class Derived2 : public Base {
virtual bool acceptsData(char*) { /* do something else */}
}
Base* createStuff(char* data)
{
Base* d1 = new Derived1();
if(d1->acceptsData(data))
{
return d1;
}
delete d1;
Base* d2 = new Derived2();
if(d2->acceptsData(data))
{
return d2;
}
delete d2;
// and more ...
}
// .... somewhere later
int main()
{
Base* Aclass = createStuff("abc");
}
我想摆脱这个长if() ...
构造,并使用一些更通用的模式,但我仍然没有经理想出一些有用的东西。有没有更好的方法呢?
答案 0 :(得分:4)
如果您想要分解代码,因为您有几个派生类,您可以使用以下内容:
namespace detail
{
template <typename T> std::unique_ptr<Base> make_base(const char* data)
{
std::unique_ptr<Base> base = std::make_unique<T>();
if (base->acceptsData(data)) {
return base;
}
return nullptr;
}
template <typename... Ts> std::unique_ptr<Base> createStuff(const char* data)
{
std::function<std::unique_ptr<Base>(const char*)> fs[] = { make_base<Ts>... };
for(auto& f : fs) {
auto base = f(data);
if(base) {
return base;
}
}
return nullptr;
}
}
Base* createStuff(const char* data) {
return detail::createStuff<Derived1, Derived2/* and other Derived classes*/>(data).release();
}
答案 1 :(得分:0)
您正在创建对象。 Factory或Builder适合您。
答案 2 :(得分:0)
虚拟构造函数设计模式可以满足您的要求。这就是它的样子......
#include <iostream>
#include <string>
#include <vector>
using namespace std;
class Base {
Base* b;
// suppress the usual constructors
Base(Base&);
Base operator=(Base&);
protected:
Base() { b = 0; };
public:
virtual void Print() { b->Print(); }
virtual ~Base() {
if (b) {
delete b;
}
}
Base(string type);
};
class Derived1 : public Base {
Derived1(Derived1&);
Derived1 operator=(Derived1&);
Derived1() {}
friend class Base;
public:
void Print() { cout << "Derived1::Print()" << endl; }
~Derived1() { }
};
class Derived2 : public Base {
Derived2(Derived2&);
Derived2 operator=(Derived2&);
Derived2() {}
friend class Base;
public:
void Print() { cout << "Derived2::Print()" << endl; }
~Derived2() { }
};
Base::Base(string type) {
if (type == "Derived1")
b = new Derived1;
else if (type == "Derived2")
b = new Derived2;
}
int main() {
vector<Base*> bases;
cout << "virtual constructor calls:" << endl;
bases.push_back(new Base("Derived2"));
bases.push_back(new Base("Derived1"));
bases.push_back(new Base("Derived1"));
bases.push_back(new Base("Derived2"));
for (int i = 0; i < bases.size(); i++) {
bases[i]->Print();
}
cout << "destructor calls:" << endl;
for (int j = 0; j < bases.size(); j++) {
delete bases[j];
}
// system("pause");
return 0;
}