What is the most graceful way to write unreachable else block

Question

For example. (in Pseudo language)

if ( a == 1 || a == 2 || a == 3 ) {
   ... some unrelated pre handling ...
   if (a == 1) {
      ...
   } else if( a == 2) {
      ...
   } else if( a == 3) {
      ...
   } else {
     ///////////// this is the unreachable else branch /////////
   }
   ... some unrelated post handling ...
}

I know I could just turn the last else if into else, but that would be not clear for reviewers.

if ( a == 1 || a == 2 || a == 3 ) {
   ... some unrelated pre handling ...
   if (a == 1) {
      ...
   } else if( a == 2) {
      ...
   } else { // this will be a == 3, but once I change the outer `a == 1 || a == 2 || a == 3` then here may be forgotten to change.
      ...
   }
   ... some unrelated post handling ...
}

Also, I could throw exception in the else block, but seems dumb,

if ( a == 1 || a == 2 || a == 3 ) {
   ... some unrelated pre handling ...
   if (a == 1) {
      ...
   } else if( a == 2) {
      ...
   } else if( a == 3) {
      ...
   } else {
     throw "unexpected case";
   }
   ... some unrelated post handling ...
}

EDIT: using switch ... case ... default does not change much, the default will be the useless branch.

Any better idea?

I'm not sure about the problem you have. Why do you need to write code which can't be reached? Or is it about catching e.g. invalid input? — Some programmer dude, Aug 21 '21 at 07:39
@Someprogrammerdude it is not a problem. I could change the last `else if (a==3)` into `else` so that no unreachable branch, but once I do that, when later someone look at the `else` block, to figure out what kind of cases it will be he has to look at the outer `if (a == 1 || a == 2 || a == 3)` to know oh the `else` just means `a==3`, this is not good for reviewers. In other words, an uneasy-to-figure-out `else` is not good, but if I write the `else`, due to the outer `if (a==1||a==2||a==3)`, the `else` become useless, so I'd like to know if there is any elegant way, without throwing exception — osexp2000, Aug 21 '21 at 08:03

score 0 · Answer 1 · answered Aug 21 '21 at 07:36

0

Depending on the actual language you, you could use a switxh statement. In that case, the "unreachable" else block would be the default case.

answered Aug 21 '21 at 07:36

aaronlukacs

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What is the most graceful way to write unreachable else block

1 Answers1