[Boost-users] Re: Any constructor evaluation in compile time?

From: David Abrahams (dave_at_[hidden])
Date: 2005-03-03 10:13:19

"Yutaka Leon Suematsu" <yutaka_at_[hidden]> writes:

> Hi everyone,
>
> I am new at the excellent Boost library. It is an incredible source of smart
> techniques and ticks.
>
> I would like to ask if there is a way to evaluate, in compile time, the
> existence of a specific constructor, except from the constructor default and
> copy constructor (I know the functions has_trivial_constructor and
> has_trivial_copy from the type_traits library). For example in the following
> code, I would like to evaluate the existence of both "A(const Config&
> config)" 

   You can do something like this with is_convertible<Config,A>

> and " template <class Random> A(const Config& config, Random&
> random) " constructors.

   This one there's no known technique for.

> Class A
> {
>   A(){.}
>   A(const Config& config){.}
>   template <class Random>
>   A(const Config& config, Random random){.}
> .
> }
>
> Also, I would like to know why and how the has_trivial_constructor works.

When it works, it relies on implementation-specific magic help from
the compiler.

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com