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Subject: Re: [boost] [review] string convert
From: Jeff Flinn (TriumphSprint2000_at_[hidden])
Date: 2011-05-05 11:17:19

Matt Chambers wrote:
> On 5/5/2011 6:48 AM, Stewart, Robert wrote:
>> Your use case is the following, right?
>> optional<int> o(try_convert_cast<int>(str));
>> int i;
>> if (!o)
>> {
>> std::cout<< "using fallback\n";
>> i = fallback;
>> }
>> else
>> {
>> i = o.get();
>> }
>> That's clearly inconvenient and 5 doesn't apply because the optional
>> won't be set if the conversion fails. To address such inconvenience,
>> you offered convert<T>::result and pair<optional<T>,bool> has been
>> suggested. Isn't optional redundant in the latter?
> What happened to:
> int i = fallback;
> if (!try_convert_to<int>(str, i)) { cout << "using fallback"; }
> A good postcondition is that try_convert_to does not modify i if the
> conversion fails. This achieves the same thing and is honestly more
> convenient and transparent than the convert<T>::result approach. I
> suppose you could argue that the preliminary assignment is inefficient,
> but I can't see a reasonable objection to it. If it really must be
> avoided, then of course for defaultable types it can look like yours
> (assigning the fallback in the if), but for non-defaultable types
> there's no benefit (a default_value<T> invocation is as bad as the
> preliminary assignment).

How would I use this within an initializer list?


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