Subject: Re: [boost] [conversion] try_lexical_cast and 200$
From: Peter Dimov (lists_at_[hidden])
Date: 2013-12-12 10:10:58
Krzysztof Czainski wrote:
> > bool parse( X& x, std::string a, std::string b )
> > {
> > return try_lexical_cast( a, x.a ) && try_lexical_cast( b, x.b );
> > }
>
> True, but I don't think you should leave it that simple. When parsing of a
> succeeds, and parsing of b fails, you get x with new value of a, and old
> value of b.
Actually you get an unspecified value in x.b, I think. Which is mirrored in
what parse does - you get an unspecified value in x when it fails. If you
want a strong guarantee:
bool parse( X& x, std::string a, std::string b )
{
X x2;
if( try_lexical_cast( a, x2.a ) && try_lexical_cast( b, x2.b ) )
{
x = x2;
return true;
}
else
{
return false;
}
}
Note that try_lexical_cast providing that same strong guarantee of leaving
"out" untouched on failure doesn't simplify the implementation of the strong
parse.