我想知道如何隐藏一个不动产字段(不是将其设为私有或公共,而是强制使用二传手和getter),并为他提供简单的二传手和getter。所以我想知道如何创建这样的 api:
private:
Property( int my_a);
public:
Property( int my_b);
...
{
set_my_a(1);
cout << get_my_a() << endl;
// my_a = 13; // will cause compiler error
...
如何通过 Boost 预处理器创建这样的东西?
你真的需要使用升压预处理器吗?您有一个没有提升的解决方案如下:
// property.h
#include <stdio.h>
#define property(type) struct : public Property <type>
template <typename T>
class Property
{
protected:
T value;
public:
virtual T get() {
return value;
}
virtual void set(T new_value) {
value = new_value;
}
};
使用示例:
// test.cpp
#include "property.h"
class Test {
public:
property(int) {} a;
property(int) {
int get() {
return value * 10;
}
} b;
property(int) {
void set(int x) {
value = x * 200;
}
} c;
property(int) {
int get() {
return value * 3000;
}
void set(int x) {
value = x * 443;
}
} d;
};
main()
{
Test t;
printf("itatbtctdtn");
for (int i=0; i<10; i++) {
t.a.set(i);
t.b.set(i);
t.c.set(i);
t.d.set(i);
printf("%it%it%it%it%in", i, t.a.get(), t.b.get(), t.c.get(), t.d.get());
}
}
http://en.wikipedia.org/wiki/Property_(programming)#C.2B.2B中的维基百科解决方案很好,但需要最少的修改才能变得有用,因为没有受保护的语句,你就无法编写自己的getter和setter。
#include <iostream>
template <typename T>
class property {
protected:
T value;
public:
T & operator = (const T &i) {
::std::cout << i << ::std::endl;
return value = i;
}
operator T const & () const {
return value;
}
};
struct Bar {
property <bool> alpha;
struct :public property <int> {
int & operator = (const int &i) {
::std::cout << "new setter " << i << ::std::endl;
return value = i;
}
} bravo;
};
main()
{
Bar b;
b.alpha = false;
b.bravo = (unsigned int) 1;
}
如果需要,您可以再更改一点:
#include <iostream>
#define SETTER(type) public: type& operator=(const type new_value)
#define GETTER(type) public: operator type const & () const
template <typename T>
class Property {
protected:
T value;
public:
T & operator = (const T &i) {
::std::cout << i << ::std::endl;
return value = i;
}
template <typename T2> T2 & operator = (const T2 &i) {
::std::cout << "T2: " << i << ::std::endl;
T2 &guard = value;
throw guard; // Never reached.
}
operator T const & () const {
return value;
}
};
struct Bar {
Property <bool> alpha;
struct:Property <int> {
SETTER(int) {
value = new_value * 1000;
::std::cout << "new method " << new_value << ::std::endl;
return value;
}
GETTER(int) {
return value/1000;
}
} bravo;
};
main()
{
Bar b;
b.alpha = false;
b.bravo = (unsigned int) 1;
::std::cout << b.bravo << ::std::endl;
}
与其重写一个实现示例,不如说这是维基百科上一个链接:http://en.wikipedia.org/wiki/Property_(programming)#C.2B.2B
这基本上强制通过 getter/setter 方法访问属性。获得所需效果所需的升级是能够将函子传递给这些属性。关于实施这些有很多想法;我不能建议的最佳方法,取决于您的发展需求。就个人而言,感觉就像过度工程化,更喜欢只使用 Pimpl 来隐藏我的私人详细信息,并明确地提供 getter/setter。