26th October 2022, 3 min read

Book Review : Template Metaprogramming with C++

3 thoughts on “Book Review : Template Metaprogramming with C++”

1. Denis says:
   October 26, 2022 at 8:05 pm

   “Up until recently, you could not mix templates and lambdas, but now you can with C++20:”

   You could since C++14.
   
int g(int x, int y) {
auto lambda = [](auto x, auto y) { return x + y; };
return lambda(x, y);
}

   It’s the same as
   https://godbolt.org/z/f59cezsje

   1. Jonathan O'Connor says:
      November 3, 2022 at 9:41 am

      I think the change in C++20 was to make it easier to get the type of x and y. Before C++20, you’d need the following code:
      
int g(int x, int y) {
auto lambda = [](auto x, auto y) {
using T = decltype(x);
return T(x + y);
};
return lambda(x, y);
}


      C++20 allows the following:
      
int g(int x, int y) {
auto lambda = [](T x, T y) {
return T(x + y);
};
return lambda(x, y);
}


      This last example also ensures that x and y have the same type, which the C++14 example does not.

2. Denis says:
   October 26, 2022 at 8:06 pm

   “Up until recently, you could not mix templates and lambdas, but now you can with C++20:”

   You could since C++14.
   
int g(int x, int y) {
auto lambda = [](auto x, auto y) { return x + y; };
return lambda(x, y);
}

   It’s the same as
   
[](T1 x, T2 y) { return x + y; };

   however, hence the C++20 syntax.
   https://godbolt.org/z/f59cezsje