Pass a custom comparator through a function

问题

I have a class with a function

MyClass::doStuff(std::vector<MyCustomData*> toSort) { ...

in which I call

std::sort(toSort.begin(), toSort.end(), MyClass::SortByZ());

myClass::SortByZ() is a custom comparator. Now this works but I would like to achieve the following:

I have several classes, which should each have its own comparator functor to sort "MyCustomData". So e.g. Class1... should have

class Class1 {
    struct SortData {
        bool operator ()(MyCustomData *lhs, MyCustomData *rhs) {
        return lhs->something1 > rhs->something1;
        }
    };
    //...many more functions/vars
}

while Class2 has a different comparator functor for the same datatype eg

class Class2 {
    struct SortData {
        bool operator ()(MyCustomData *lhs, MyCustomData *rhs) {
        return lhs->something2 > rhs->something2;
        }
    };
    //...many more functions/vars
}

Now I would like to be able to call the function MyClass::doStuff(...) with either

doStuff(myData, Class1::SortData)

doStuff(myData, Class2::SortData)

and the function MyClass::doStuff(...) should use the respective Sort-Order.

I did not find out a way of doing this, is there one? I would like a simple solution (doesn't have to support templates or anything). I would be willing to use boost if I needed that, but a solution without boost would be preferred.

I hope I was able to describe what I want to achieve? Thanks for any help!

回答1:

You will have to make doStuff a template:

template <typename Comparator>
void doStuff(std::vector<MyCustomData*> toSort, Comparator compare) {
   // ...
   std::sort(toSort.begin(), toSort.end(), compare);
   // ...
}

Also, it might want to take the first argument by reference. As it is, it will sort a copy of the argument, discard that copy, and leave the caller's vector untouched; although perhaps that's what you want.

回答2:

Use a function template, in order to accept any kind of comparison function (or functor):

template <typename Comparator>
void doStuff(std::vector<MyCustomData> toSort, Comparator comparator)
{
    ...
    std::sort(toSort.begin(), toSort.end(), comparator);
    ...
}
...
doStuff(myData, Class1::SortData());
doStuff(myData, Class2::SortData());

This is how standard algorithms provide genericity.

来源：https://stackoverflow.com/questions/10245728/pass-a-custom-comparator-through-a-function

标签

c++

comparator