Here is my code:
class Test
{
private:
SomeType a;
public:
using TE = decltype(a.find("abc")->second);
TE getElement(const string &) const;
};
Test::TE Test::getElement(const string & key) const
{
return a.find(key)->second;
}
In the class, a function can return an element of a like above. The type of a.find(key)->second is very complicated so I don't want to type it all. In fact, I even don't know how to type it...
So I want to use decltype like above but failed. Here is the error:
error C2227: left of '->second' must point to class/struct/union/generic type
You have to either move the definition of a up:
class Test
{
private:
SomeType a;
public:
using T = decltype(a.find("abc")->second);
...
};
Or, instead of a, substitute and expression of the correct type using std::declval:
class Test
{
public:
using T = decltype(std::declval<SomeType&>().find("abc")->second);
...
private:
SomeType a;
};
Note that you're missing a > here:
return a.find(key)-second;
^^^
And that your decltype() expression is looking up a const char[4] instead of a std::string const &. So the most correct version would be:
using T = decltype(std::declval<SomeType&>().find(
std::declval<std::string const&>()
)->second);
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