如何使用初始化程序列表初始化2D向量成員？

Question

我的代碼：

#include <initializer_list> 
#include <vector>  

class Foo { 
    std::vector<std::vector<int> > data; 
    public: 
    Foo(std::initializer_list<std::initializer_list<int> > & data) : data(data) {} 
}; 

int main(){ 
    Foo f {{1,2},{3,3}}; 
    return 0; 
} 

，編譯器抱怨：

initalizer_list_test.cpp: In constructor ‘Foo::Foo(std::initializer_list<std::initializer_list<int> >&)’: 
initalizer_list_test.cpp:11:79: error: no matching function for call to ‘std::vector<std::vector<int> >::vector(std::initializer_list<std::initializer_list<int> >&)’ 
    Foo(std::initializer_list<std::initializer_list<int> > & data) : data(data) {} 
                      ^
initalizer_list_test.cpp:11:79: note: candidates are: 
In file included from /usr/include/c++/4.8.2/vector:64:0, 
       from initalizer_list_test.cpp:2: 
/usr/include/c++/4.8.2/bits/stl_vector.h:392:9: note: template<class _InputIterator, class> std::vector<_Tp, _Alloc>::vector(_InputIterator, _InputIterator, const allocator_type&) 
     vector(_InputIterator __first, _InputIterator __last, 
     ^
/usr/include/c++/4.8.2/bits/stl_vector.h:392:9: note: template argument deduction/substitution failed: 
initalizer_list_test.cpp:11:79: note: candidate expects 3 arguments, 1 provided 
    Foo(std::initializer_list<std::initializer_list<int> > & data) : data(data) {} 

如何讓它正常工作？

Answer 1

首先，使用矢量的初始化列表來初始化2D矢量。然後，只需把它按值而不是按引用（初始化列表，就我所知，通常是按值傳遞和非const引用將無法正常工作）：

Foo(std::initializer_list<std::vector<int> > data) : data(data) {}