c++ - Lambda作为成员函数模板的默认参数

头文件

#include <functional>

struct Check {};
struct Entry {};
struct Table {};

class SeatEntries
{
public:
    // does not compile!
    template<class T>
    void Populate(T from,
                  std::function<bool (Entry *)> predicate = [] (Entry *) { return true; },
                  std::function<void (Entry *)> action = [] (Entry *) {})
    {
        Reset();
        PopulateImpl(from, predicate, action);
    }

    // compiles!
    void PopulateFromCheck(Check *from,
                  std::function<bool (Entry *)> predicate = [] (Entry *) { return true; },
                  std::function<void (Entry *)> action = [] (Entry *) {})
    {
        Reset();
        //PopulateImpl(from, predicate, action);
    }

    void Reset();

private:
    template<class T>
    void PopulateImpl(T from,
                      std::function<bool (Entry *)> predicate,
                      std::function<void (Entry *)> action);
};

template<>
void SeatEntries::PopulateImpl<Table *>(Table *from, std::function<bool (Entry *)> predicate, std::function<void (Entry *)> action);

template<>
void SeatEntries::PopulateImpl<Check *>(Check *from, std::function<bool (Entry *)> predicate, std::function<void (Entry *)> action);

题

为什么第一个成员函数模板不编译？这是VS2012和gcc 4.8.1中的错误吗？我是否不了解有关成员函数模板和lambda作为默认参数的某些事实？

VS2012输出

error C2958: the left parenthesis '(' found at 'seathelpers.h(33)' was not matched correctly
error C2988: unrecognizable template declaration/definition
error C2059: syntax error : '{'
error C2334: unexpected token(s) preceding '{'; skipping apparent function body

引用的左括号是Populate()函数模板的左括号。

GCC 4.8.1(MinGW)

Test.h:13:66: internal compiler error: in push_class_level_binding_1, at cp/name-lookup.c:3019
    std::function<bool (Entry *)> predicate = [] (Entry *) { return true; },
                                               ^

最佳答案

我能够使用gcc 4.8.3正确编译以上代码

$ g++ --version
g++ (GCC) 4.8.3 20140624 (Red Hat 4.8.3-1)