interface identity (was Re: Proposed new dependency: github.com/juju/errors (and github.com/juju/errgo))

[Tim Penhey]

On 28/05/14 13:31, Nate Finch wrote:
> If you're talking about errgo, if all we care about is transition, but
> not what the actual types are, we could just record in the list when we
> mask the type.

We could, but that would mean walking the list every time you want to
check the cause.  It would also change the meaning of cause, so a nil
cause means get the cause from the previous (underlying) error.

Do you not agree with me though that in the general Go language there
should be a way to check identity? Or do you not agree?

Tim

> 
> On May 27, 2014 8:48 PM, "Tim Penhey" <tim.penhey at canonical.com
> <mailto:tim.penhey at canonical.com>> wrote:
> 
>     On 28/05/14 12:43, Nate Finch wrote:
>     > This sounds like one of those "if you have to ask this question,
>     you're
>     > doing something wrong".
>     >
>     > Can you give an example of where we need this?
> 
>     Sure... let's say we have a stack of errors, for simplicity of the
>     argument lets say it is a slice of error interface values.
> 
>      stack []error
> 
>      * an error is pushed on to the stack initially, we now have one error
>      * the same error is pushed (or appended - I don't care)
>      * we now have the same error twice
>      * I push a new error on the stack, so it looks a little like this
>        [err1, err1, err2] right?
> 
>     Now iterating through this slice I want to know when the error changes.
> 
>     There seems to be no clean way to do this.
> 
>     Tim
> 
>