CODEWITHSUNDEEP
c++templatesc++17
Rud48
Rud48

Reputation: 885

Name Instances of Class Member Template Function

Consider this code which obviously doesn't work but illustrates what I want to do.

struct C {
   template <int I>
   void f(float x) {...}
...
   using one = f<1>;
   using two = f<2>;
};

C c;
c.one(4.0f);
c.two(77.0f);

There a 10 member functions for my class that can take 2 value, not type, template parameters and I want to give them distinct names so the user doesn't have to type in the template parameters. This is illustrated by one and two above.

Any ideas how to do this with C++17, or even C++20?

Update:

Nice answer below but as mentioned a bit verbose. I'm trying to avoid:

void one(float v) { 
   f<1>(v); 
   }

although my actual statements would be slightly longer.

Hoped something concise was available.

Upvotes: 2

Views: 75

Answers (2)

max66
max66

Reputation: 66200

If you accept to call one and two with a little different syntax

(c.*one)(4.0f);
(c.*two)(77.0f);

you can declare one and two as (constant, if you want) pointers to methods of C.

I mean... outside C you can write

using mftype = void(C::*)(float);

constexpr mftype one = &C::f<1>;
constexpr mftype two = &C::f<2>;

The following is a full compiling example

#include <iostream>

struct C
 {
   template <int I>
   void f (float x)
    { std::cout << (x+I) << std::endl; }
 };

using mftype = void(C::*)(float);

constexpr mftype one = &C::f<1>;
constexpr mftype two = &C::f<2>;

int main ()
 {
   C c;

   (c.*one)(4.0f);
   (c.*two)(77.0f);
 }

Upvotes: 2

StoryTeller - Unslander Monica
StoryTeller - Unslander Monica

Reputation: 170064

You can't alias member functions directly. But you can write wrappers that forward to them:

template<typename... Args>
decltype(auto) one(Args&& ...args) { return f<1>((Args&&)args...); }

template<typename... Args>
decltype(auto) two(Args&& ...args) { return f<2>((Args&&)args...); }

Here it is live

A little verbose to write, but does provide the simplicity you want for the client programmer.

Upvotes: 3

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