On Tue, Jan 13, 2009 at 3:50 PM, Chris Weed <chrisweed@gmail.com> wrote:
On Tue, Jan 13, 2009 at 7:26 AM, Vladimir Batov <batov@people.net.au> wrote:
I use boost::lexical_cast quite a bit. Possibly due to specifics of my
task I constantly stumble upon two things:
1. It throws if/when conversion fails; 2. It requires the 'Target' class to be default-constructible.
I'd like to suggest extending the existing
template<class Target, class Source> Target lexical_cast(Source const& arg)
interface with
template<class Target, class Source> Target lexical_cast(Source const& arg, Target const& failure_value)
The behavior of the latter would be to return the 'failure_value' if/when
the conversion fails. That communicates the fact of the conversion failure differently (without an exception thrown), i.e. its usage would be as following:
int value = boost::lexical_cast(some-string, -1); if (value == -1) conversion failed.
In fact, my usage pattern is such that I often do not even need to check
the success of the conversion -- if the conversion fails, the supplied failure/default value is returned/used and proceeded with.
This doesn't look like a good interface due to using a casted value as a "null"-code. This code would fail when "-1" is a value of some-string. This could lead to very big problems! I would suggest something more like boost::optional<int> value = boost::lexical_cast(some-string,boost::no_throw); if(!value) conversion failed.
I prefer the original suggestion of providing a failure value for most of my uses because: 1. Often I do not want to check an error, I have a value in mind to use in the case of error 2. It removes the requirment for a default constructor I see that if we need to handle an error condition then the ability to return an optional<Target> is a good plan. Perhaps two new overloads would be optimal? Neil Groves
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