[jira] [Updated] (MESOS-3754) Update the style guide with a rule around the use of default case in switch statements

["Michael Park (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/MESOS-3754?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Michael Park updated MESOS-3754:
--------------------------------
    Summary: Update the style guide with a rule around the use of default case in switch statements  (was: Update the style guide to omit the default case in switch statements)

> Update the style guide with a rule around the use of default case in switch statements
> --------------------------------------------------------------------------------------
>
>                 Key: MESOS-3754
>                 URL: https://issues.apache.org/jira/browse/MESOS-3754
>             Project: Mesos
>          Issue Type: Bug
>          Components: documentation
>            Reporter: Michael Park
>
> This is the continuation of the initial discussions started on MESOS-2664.
> The motivation is to rely on the compiler for compile-time errors for cases missing in the {{switch}} statement, rather than aborting in the {{default}} case at runtime.
> The pattern we want to avoid is a {{switch}} statement that fully enumerates the cases of an {{enum}} *and* having a {{default}} case that aborts at runtime. The preferred approach is to omit the {{default}} case.
> This pattern can be seen across the codebase, one example is:
> {code}
> switch (volume.mode()) {
>   case Volume::RW: volumeConfig += ":rw"; break;
>   case Volume::RO: volumeConfig += ":ro"; break;
>   default:
>     LOG(FATAL) << "Unknown Volume mode: " << volume.mode();
>     break;
> }
> {code}
> The proposal is not to disallow uses of {{default}} cases, but to only use them when it actually carries some meaningful fallback behavior.
> This use of {{default}} leads to the following advantages:
> 1. If we miss any of the cases, you get notified via a compiler-error.
> 2. If a new value is added to an {{enum}}, the compiler reports all of the places that needs to be updated to handle the new value.
> Ideally, the compiler would also prevent us from covering all enumerations *and* providing a {{default}}. Since this is not an available option, we aim to capture this as a style guideline.



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