c++ - std::map 与 lambda 比较器

Question

我下面的代码给我编译器错误，我不明白我在做什么错。有人可以帮忙吗？

基本上我想做的就是通过引用一个函数来填充一个 STL map 容器。这个 map 容器还有一个与之关联的比较器 lambda。

#include "stdafx.h"
#include <functional>
#include <map>

using namespace std;

typedef struct _tagAddressBook
{
  string strFirstName;
  string strLastName;
  long nZipCode;
} AddressBook;

void foo(map<string, AddressBook, function<bool(const string&, const string&)>> &myAddressBook)
{
  AddressBook addressBookInstance;
  addressBookInstance.strFirstName = "Bob";
  addressBookInstance.strLastName = "Parker";
  addressBookInstance.nZipCode = 12345;

  myAddressBook.insert(std::pair<string, AddressBook>(addressBookInstance.strFirstName, addressBookInstance));
}

int _tmain(int argc, _TCHAR* argv[])
{
  auto myComparator = [] (const string &strLeft, const string &strRight) { return(strLeft.compare(strRight) <= 0 ? true : false); };
  map<string, AddressBook, decltype(myComparator)> myAddressBook(myComparator);

  foo(myAddressBook);

    return 0;
}

我在 VS2012 上得到以下编译错误

错误 1 ​​错误 C2664:“foo”:无法将参数 1 从“std::map<_Kty,_Ty,_Pr>”转换为“std::map<_Kty,_Ty,_Pr> &”d:\my projects\mapwithlambdacomparator\mapwithlambdacomparator\mapwithlambdacomparator.cpp 32

2   IntelliSense: a reference of type "std::map<std::string, AddressBook, std::function<bool (const std::string &, const std::string &)>, std::allocator<std::pair<const std::string, AddressBook>>> &" (not const-qualified) cannot be initialized with a value of type "std::map<std::string, AddressBook, lambda []bool (const std::string &strLeft, const std::string &strRight)->bool, std::allocator<std::pair<const std::string, AddressBook>>>" d:\My Projects\MapWithLambdaComparator\MapWithLambdaComparator\MapWithLambdaComparator.cpp  32

Answer 1

Lambda 函数与 std::function 无关。事实上，每个都是它自己的类类型。如果你想做看起来你做的事，你可以通过 foo 模板来做，然后让演绎来解决它。

template <typename Cmp>
void foo(map<std::string, AddressBook, Cmp> &myAddressBook)
{
    AddressBook addressBookInstance;
    addressBookInstance.strFirstName = "Bob";
    addressBookInstance.strLastName = "Parker";
    addressBookInstance.nZipCode = 12345;

    myAddressBook.insert(std::pair<string, AddressBook>(addressBookInstance.strFirstName, addressBookInstance));
}

这适用于我的工具链，“Apple LLVM 版本 5.0 (clang-500.2.75)(基于 LLVM 3.3svn)”。我认为没有理由它也不能与您的工具链一起使用。