Re: [boost] [err] RFC

Subject: Re: [boost] [err] RFC
From: Gavin Lambert (gavinl_at_[hidden])
Date: 2015-11-19 17:06:54

On 20/11/2015 04:58, Domagoj Šarić wrote:

>> The more problematic case is if the combiner was not expecting
>> failure, and so someone used the same expression with a combiner that
>> accepted T.   So the compiler calls all three calc methods
>> (constructing fallible_result<T>s along the way), then gets around to
>> converting the first one back to T, which throws.  This is ok, but
>> then the other two are destroyed; and if at least one of these throws
>> too, then you're dead.
>
> As explained before this cannot happen as even the implicit conversion
> operators work only on rvalues...

The result of a function call that returns either a bare T or a T&& is 
an rvalue.

Your asserts will prevent this particular usage, but that's the only 
thing that does.  And asserts don't fire until runtime, so if it's an 
infrequently exercised path (without a unit test) this may go unnoticed 
for quite a while.  Especially if people are in the habit of testing 
release builds (which is not that uncommon).