Re: [boost] Noexcept

Subject: Re: [boost] Noexcept
From: Emil Dotchevski (emildotchevski_at_[hidden])
Date: 2017-06-13 21:19:30

On Tue, Jun 13, 2017 at 11:01 AM, Peter Dimov via Boost <
boost_at_[hidden]> wrote:

> Emil Dotchevski wrote:
>
>> If error codes are treated as "the error", then the error domain is
>> limited to a single function. Consider these two functions:
>>
>> int f1(....); //returns 0 on success, 1-f1_error1, 2-f1_error2
>> int f2(....); //returns 0 on success, 1-f2_error1, 2-f2_error2
>>
>> If f2 calls f1, if the error is communicated by an error code, f2 _must_
>> translate the error condition from the domain of f1 errors, to the domain
>> of f2 errors. And this must be done at every level, which introduces many
>> points in the code where subtle errors may occur, and that is in error
>> handling code which is very difficult to test and debug.
>>
>
> That's exactly the problem std::error_code solves, as it's a (code,
> domain) pair, so there's no need to translate.
>

That presumes that ENOENT represents the same _error_ when returned from
two different functions. Generally, it does not. The correct strategy in
C++ is to throw different types to indicate different errors, even when
both end up carrying the same ENOENT.

So it is critical to decouple the error code (std or otherwise) from _what_
went wrong, and if you don't, you're butchering the ability to write
error-neutral functions, which in practice means translating error codes
from one domain to another, at every level, which is prone to errors.