Re: [boost] Boost.Hana - Type Classes, data types and categories (tags).

Subject: Re: [boost] Boost.Hana - Type Classes, data types and categories (tags).
From: Niall Douglas (s_sourceforge_at_[hidden])
Date: 2014-09-23 07:25:45

On 20 Sep 2014 at 17:13, Benedek Thaler wrote:

> I'm not sure what Niall is referring to, but namespaces come into handy
> when using the swap trick described in effective STL:
> 
> template<typename T>
> library_function(T& a, T& b)
> {
>   using std::swap;
>   swap(a,b); // will use specialized swap in namespace of T if available
> }

I'm not a fan of publicly exposed ADL usage personally. It's too 
brittle - the non-specialised swap may get called inadvertently and 
performance suffer in a highly unobvious way to detect. For example, 
if T is not perfectly a type in namespace X (e.g. it's a trivial 
descendent), any X::swap() will *not* get invoked even when it would 
make absolute sense.

I am personally a huge fan of when expected optimisations fail to 
apply, it should never be silent. Preferably a compile time error, 
but I am not adverse to an abort() either.

Niall

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