C++ typed variables using struct

Question

In C++ I want to create a typed variable that won't accidentally be used or converted to some other type. What I've come up with is:

struct  DId {
    uint32_t    v;  
    DId (uint32_t i = 0)    
    {   
        v   =   i;  
    }
};

struct  TId {   
    uint32_t    v;  
    TId (uint32_t i = 0)    
    {   
        v   =   i;  
    }
};

This seems to work, though sometimes I need to directly access the value, but are there any other methods I really should define? Does it use any extra resources at run time? (I could use preprocesser commands to switch it out with a "using TId = uint32_t" if not in debug mode, though that would mean extra work whenever I need to directly access the value.)

Or is there some better approach that I just haven't noticed?

Sounds like you want a [scoped enumeration](https://en.cppreference.com/w/cpp/language/enum#Scoped_enumerations), though these don't really work well for arbitrary values, only for avoiding implicit conversion to other types. — Patrick Roberts, Nov 30 '21 at 05:23
@PatrickRoberts why do you think the post is about *implicit* casts? — OrenIshShalom, Nov 30 '21 at 05:25
using empty struct as a tag. ` template struct Id { uint32_t v; TId (uint32_t i = 0) { v = i; } }; struct TT{}; Idid(1); ` like this? — Nimrod, Nov 30 '21 at 05:33
https://www.fluentcpp.com/2016/12/08/strong-types-for-strong-interfaces/ — doug, Nov 30 '21 at 05:35
You are looking for "strong typedef". Boost has it, your solution is Ok too. Don't bother with doing something else in release mode, there is no overhead. — n. m. could be an AI, Nov 30 '21 at 05:41
probably a duplicate of: https://stackoverflow.com/questions/34287842/strongly-typed-using-and-typedef can someone take a look? — OrenIshShalom, Nov 30 '21 at 05:43
The code to go along with the article from @doug https://github.com/joboccara/NamedType — Fantastic Mr Fox, Nov 30 '21 at 06:20

score 0 · Accepted Answer · answered Nov 30 '21 at 14:18

You may make the structure templated so that it can be used at multiple places and define a typecast operator.

template<typename T>
struct Id {
  T v;  
  Id (T i = T{}) { v = i; }. // Ideally not required
  operator T () { return v; } // optional to allow conversion to T
};

using DId = Id<uint32_t>;

Your code as it is also fine. Above way is for better utilization and avoid repetition.

C++ typed variables using struct

1 Answers1