Alternatives to exceptions for error handling

[Jacob Carlborg]

On Monday, 30 November 2020 at 11:43:01 UTC, Ola Fosheim Grøstad 
wrote:

> But they are also a bit too simple. Like, if accessing external 
> resources you often want to do retries. Annoying to throw all 
> the way out.
>
> Consider for instance if you try to fetch a file from an url, 
> then it fails. It would have been nice to inject a recovery 
> handler that can analyze the failure and provide a new url, 
> sleep then retry etc.
>
> e.g. something along the lines of this sketch:
>
> fetch_url(url) {
>   retry with (url) {
>    …download attempt…
>    …throw http_fail, server_busy…
>   } catch (…){
>    …ok cleanup, nobody wanted a retry…
>   }
> }
>
>
> main(){
>   on http_fail(url){
>     url = replace_with_backup_server(url)
>     return true; // retry
>   }
>   data = fetch_url(url)
>   …
> }

In Ruby there's the `retry` keyword for this. Although you cannot 
control the recovery handler from the outside, like in your 
example. In D terms you would put `retry` in a `catch` block and 
it would run the code inside the `try` block again.

--
/Jacob Carlborg