Re: [Boost-users] BOOST_STRONG_TYPEDEF

Subject: Re: [Boost-users] BOOST_STRONG_TYPEDEF
From: Agustín K-ballo Bergé (kaballo86_at_[hidden])
Date: 2014-08-07 21:11:40

On 07/08/2014 09:40 p.m., Jono Poff wrote:
> Hi,
>
> compiling this program with g++ 4.7.1 ...
>
>
>              #include <boost/serialization/strong_typedef.hpp>
>              BOOST_STRONG_TYPEDEF(uint32_t, LINKID_T)
>
>              int main()
>              {
>                  LINKID_T lid = 0xffddee33;
>                  return 0;
>              }
>
> I get
>
>
>              error: conversion from 'unsigned int' to non-scalar type
> 'LINKID_T' requested
>
>
> Looking at the header, the strong typedef struct defines assignment from
> uint32_t to LINKID_T ...
>
>
>              D & operator=(const T & rhs) { t = rhs; return *this;}
>
>
> ... so what gives?

The expression `LINKID_T lid = 0xffddee33;` would be doing construction, 
not assignment. The constructor that would be picked would be the 
conversion construction `explicit D(const T t_) : t(t_) {};` followed by 
the copy construction `D(const D & t_) : t(t_.t){}`, but the conversion 
constructor is not viable because it is `explicit`.

What you can do is either:

     LINKID_T lid = LINKID_T(0xffddee33);

or simply:

     LINKID_T lid(0xffddee33);

Regards,
-- 
Agustín K-ballo Bergé.-
http://talesofcpp.fusionfenix.com