Re: [Boost-users] Optionally enforce const correctness in argument dependent lookup

Subject: Re: [Boost-users] Optionally enforce const correctness in argument dependent lookup
From: Steven Watanabe (watanabesj_at_[hidden])
Date: 2009-01-17 23:36:25

AMDG

er wrote:
> The example below illustrates my intent, but obviously it's not the 
> right approach... so I'm hoping someone has a suggestion.
>
> template<typename X>
> struct enforce_constness{ typedef add_reference<const X> type; };
>
> template<template<typename> class T = enforce_constness>
> struct A{
>
>  template<typename X>
>  void operator()(typename T<X>::type x)const{
>      // Under default I'd like const X&
>  };
>
> }
>
> X x; A<> a; a(x);
>
> no match for call to (A<T>)(X&)

It's impossible to deduce what the template parameter should be.

The easiest way is to use a forwarding function that optionally adds const.
template<typename X>
void call_impl(X& x) const;

template<typename X>
void operator()(const X& x) { return(call_impl(x)); }
template<typename X>
void operator()(X& x) { return(call_impl(static_cast<typename 
T<X>::type>(x))); }

BTW, your subject line is a bit misleading because this has nothing to
do with ADL

In Christ,
Steven Watanabe