I am trying to call a particular member function in all elements of a tuple using std::apply. This works when I use a lambda but not when defining a free function.

Following Template tuple – calling a function on each element the following code works when using a lambda:

#include<tuple>
#include<iostream>

struct Double  {
     void print() { std::cout << "Double!" << std::endl;}
};

struct Vector  {
    void print() { std::cout << "Vector!" << std::endl;}
};

template<class ...T>
void printAll2(T &...x){(x.print(), ...);}

int main() {

    auto workspace = std::make_tuple<Vector, Double, Vector>({},{},{});
    auto printAll = [](auto &...x){(x.print(), ...);};

    std::apply(printAll , workspace);

    // This does not work.
    //std::apply(printAll2, workspace);

    return 0;
}

However, when I try to use the free function printAll2 I get an error:

<source>:22:5: error: no matching function for call to 'apply'
   22 |     std::apply(printAll2, workspace);
      |     ^~~~~~~~~~
/opt/compiler-explorer/gcc-snapshot/lib/gcc/x86_64-linux-gnu/15.0.0/../../../../include/c++/15.0.0/    tuple:2955:5: note: candidate template ignored: couldn't infer template argument '_Fn'
 2955 |     apply(_Fn&& __f, _Tuple&& __t)
      |     ^
1 error generated.
Compiler returned: 1

What is the difference between the lambda and the function?

Many thanks!