如何重构我的库以包含模板？

Question

I am trying to add template functionality to my vector class, after already having used it without templates throughout my project.

The old version used hardcoded float to save the values for x , y and z . What I am trying to do now is to make the class also be able to use double through a template.

My class definition looks like this:

namespace alg {

template <class T=float> // <- note the default type specification
struct vector
{
    T x, y, z;
    vector() : x(0), y(0), z(0) {}
    explicit vector(T f) : x(f), y(f), z(f) {}
    vector(T x, T y, T z) : x(x), y(y), z(z) {}

    // etc
};

}

I was hoping to now be able to compile my project without making changes to the code in it, by telling the template to use float per default if no template parameter is given.

However, I am still getting errors about missing template arguments...

#include "vector.hpp"

int main() {
    alg::vector a;
    return 0;
}

--

$ g++ -O3 -Wall -Wextra -std=gnu++0x test.cpp
test.cpp: In function ‘int main()’:
test.cpp:4:17: error: missing template arguments before ‘a’
test.cpp:4:17: error: expected ‘;’ before ‘a’

How can I make this code work without changing test.cpp ? Preferably without mangling the struct name and using typedef

Answer 1

Referring to a class template without angle brackets is illegal, unfortunately.

The way the STL does this with std::string is like this, even though your request was "no mangling":

template <typename T> class basic_string { ... };
...
typedef basic_string<char> string; 

In your case, you would have to write vector<> everywhere, or rename your template:

template <class T>
struct basic_vector {
    ...
};

typedef basic_vector<float> vector;

Answer 2

不幸的是，即使您具有默认类型名，也必须编写alg::vector<> 。

Answer 3

in all of my experience you can't. you need to change your alg::vector to alg::vector<> which is the syntax for the default argument. although single find and replace should do this.