Re: [boost] [conversion] try_lexical_cast and 200$

Subject: Re: [boost] [conversion] try_lexical_cast and 200$
From: Gavin Lambert (gavinl_at_[hidden])
Date: 2013-12-12 02:10:25

On 12/12/2013 19:45, Quoth Michael Caisse:
> On 12/11/2013 10:34 PM, Gavin Lambert wrote:
>> Also having to specify both types is more annoying than in the bool
>> form, where the compiler can infer the parameters.
>
> You still just write:
>
>    out1 = try_lexical_cast<T1>(in1)
>
> where the type of out1 is optional<T1> and the type of in1 is deduced.

I thought that ought to work, but I wrote a toy example and it didn't, 
which is why I phrased it like that.  Thinking back on it now I realise 
what the problem was:

On 12/12/2013 18:41, Quoth Peter Dimov:
 > Antony Polukhin wrote:
 >> And if yes, what signature is preffered:
 >>
 >> bool try_lexical_cast<Out, In>(Out&, const In&)
 >> bool try_lexical_cast<Out, In>(const In&, Out&)
 >> boost::optional<Out> try_lexical_cast<Out, In>(const In&)
 >
 > bool try_lexical_cast<In, Out>(const In&, Out&), I'd say.

Inference requires the <Out, In> ordering of template parameters (for 
the optional version; it doesn't matter for the bool version).  I had 
them wrong when testing my toy.

My apologies for the noise.