Re: [boost] [review] Review of Outcome (starts Fri-19-May)

Subject: Re: [boost] [review] Review of Outcome (starts Fri-19-May)
From: Peter Dimov (lists_at_[hidden])
Date: 2017-05-21 22:14:13

Niall Douglas wrote:
...
> If there was an error, we return an error code of 
> kerneltest_errc::filesystem_comparison_internal_failure with a payload of 
> the string message from the source error and its original error code in 
> the first 32 bit code1 integer. That is used later on to print the exact 
> error code returned by the system as we know it will always be 
> system_category.
>
> If the directory structures differed, we return an error code of 
> kerneltest_errc::filesystem_comparison_failed with a payload of the string 
> of the path which did not match.
>
> Is this sufficient, or would you prefer a different example?

Thanks, that's very helpful.

The use case here is similar to std::throw_with_nested, you have an 
error_code that you are overriding with another. You could extend your ring 
buffer facility to support this natively. For that, you need to store in the 
buffer entry the error code (a duplicate of error_code_extended's members) 
_and_ the unique_id of the "parent" error_info_extended. This would allow 
you to later retrieve the whole chain of ring buffer entries (subject to 
availability.) In your example, you'd do

    testret = error_code_extended( 
kerneltest_errc::filesystem_comparison_internal_failure, 
workspaces_not_identical.error() );

Since workspaces_not_identical.error() is already in the ring buffer, you 
only need a 'pointer' to it in testret. There's also no need to pass its 
message() in testret's message, you could use that for other purposes.