C++ template and ambiguous function call

Question

Some code I have no control over has a number of overloaded functions which accepts different types

i.e.

setValue(int)
setValue(std::string)
setValue(bool)

And I have a template function which would idealy take any one of these types and pass it on to the correct setValue function.

template <class T>
do_something(T value) {
    ...
    setValue(value);

But I get this error

error: call to member function 'SetValue' is ambiguous

Is there anything I can do to work around this problem without copy and pasting my code for each type like the writers of setValue have?

What type are you trying to instantiate your template for? Most likely it's a type that there isn't an *exact* match in the overloaded functions but more than one valid conversion — jcoder, Sep 25 '13 at 08:35
@k06a awful suggestion. You could at least suggest static_cast(value) — BЈовић, Sep 25 '13 at 08:43
@user2675345 could you show us how do you call `do_something`? which type is ambiguous? — billz, Sep 25 '13 at 08:49
@billz In by answer, I show a case: `setValue(char); setValue(double);` and `do_something()` is ambiguous — Jarod42, Sep 25 '13 at 09:30

score 1 · Accepted Answer · answered Sep 25 '13 at 09:26

by defining you own SetValue with exact match and forwarding to the correct overload.

void setValue(int i) { setValue(static_cast<double>(i)) }

or (if you have a lot of "setValue" functions with same type) you may help the compiler to choose which overload to use like this:

void setValue(char a);
void setValue(double a);

template <typename T>
struct TypeToUseFor
{
    typedef T type;
};

template <>
struct TypeToUseFor<int>
{
    typedef double type;
};

template <class T>
void func(T value)
{
    setValue(static_cast<typename TypeToUseFor<T>::type>(value));
//    setValue(value);
}

int main() {
    func(0);   // int -> ?
    func('0'); // exact match
    func(0.0); // exect match
    func(0.f); // float -> double

    return 0;
}

score 0 · Answer 2 · answered Sep 25 '13 at 08:46

0

I have no problems with:

void setValue(int a)
{
}

void setValue(std::string a)
{
}

void setValue(bool a)
{
}

template <class T>
void func(T value)
{
    setValue(value);
}

int main()
{
    func(5);
}

Here is my run: http://codepad.org/1wq8qd7l

answered Sep 25 '13 at 08:46

k06a

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Yes there are no problems with this logic. It seems my problem was something slightly different. – user2675345 Sep 25 '13 at 13:44

C++ template and ambiguous function call

2 Answers2