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1.DeducingTypes/item3.md
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@ -6,7 +6,7 @@
我们将从一个简单的情况开始，没有任何令人惊讶的情况。相比模板类型推导和`auto`类型推导（参见[Item1](https://github.com/kelthuzadx/EffectiveModernCppChinese/blob/master/1.DeducingTypes/item1.md)和[Item2](https://github.com/kelthuzadx/EffectiveModernCppChinese/blob/master/1.DeducingTypes/item2.md)），`decltype`只是简单的返回名字或者表达式的类型： 我们将从一个简单的情况开始，没有任何令人惊讶的情况。相比模板类型推导和`auto`类型推导（参见[Item1](https://github.com/kelthuzadx/EffectiveModernCppChinese/blob/master/1.DeducingTypes/item1.md)和[Item2](https://github.com/kelthuzadx/EffectiveModernCppChinese/blob/master/1.DeducingTypes/item2.md)），`decltype`只是简单的返回名字或者表达式的类型：
````cpp ````cpp
const int i=0; //decltype(i)是const int const int i = 0; //decltype(i)是const int
bool f(const Widget& w); //decltype(w)是const Widget& bool f(const Widget& w); //decltype(w)是const Widget&
//decltype(f)是bool(const Widget&) //decltype(f)是bool(const Widget&)
@ -17,19 +17,19 @@ struct Point{
Widget w; //decltype(w)是Widget Widget w; //decltype(w)是Widget
if (f(w))... //decltype(f(w))是bool if (f(w))… //decltype(f(w))是bool
template<typename T> //std::vector的简化版本 template<typename T> //std::vector的简化版本
class vector{ class vector{
public: public:
... …
T& operator[](std::size_t index); T& operator[](std::size_t index);
... …
} };
vector<int> v; //decltype(v)是vector<int> vector<int> v; //decltype(v)是vector<int>
... …
if (v[0] == 0)... //decltype(v[0])是int& if (v[0] == 0)… //decltype(v[0])是int&
```` ````
看见了吧？没有任何奇怪的东西。 看见了吧？没有任何奇怪的东西。
@ -65,7 +65,7 @@ auto authAndAccess(Container& c, Index i) //不那么正确
````cpp ````cpp
std::deque<int> d; std::deque<int> d;
... …
authAndAccess(d, 5) = 10; //认证用户，返回d[5]， authAndAccess(d, 5) = 10; //认证用户，返回d[5]，
//然后把10赋值给它 //然后把10赋值给它
//无法通过编译器！ //无法通过编译器！
@ -159,13 +159,13 @@ int x = 0;
decltype(auto) f1() decltype(auto) f1()
{ {
int x = 0; int x = 0;
... …
return x; //decltype(x）是int，所以f1返回int return x; //decltype(x）是int，所以f1返回int
} }
decltype(auto) f2() decltype(auto) f2()
{ {
int x =0l; int x = 0;
return (x); //decltype((x))是int&，所以f2返回int& return (x); //decltype((x))是int&，所以f2返回int&
} }
```` ````