[jira] [Created] (MESOS-3754) Update the style guide to omit the default case in switch statements

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

Michael Park created MESOS-3754:
-----------------------------------

             Summary: Update the style guide to omit the 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.



--
This message was sent by Atlassian JIRA
(v6.3.4#6332)