Comment by xyzzyz

Comment by xyzzyz 11 hours ago

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It's actually somewhat hard to hit that panic in a realistic scenario. This is because you are unlikely to be using slice indices that are not on a character boundary. Where would you even get them from? All the standard library functions will return byte indices on a character boundary. For example, if you try to do something like slice the string between first occurrence of character 'a', and of character 'z', you'll do something like

  let start = s.find('a')?;
  let end = s.find('z')?;
  let sub = &s[start..end];
and it will never panic, because find will never return something that's not on a char boundary.
inferiorhuman 10 hours ago

  Where would you even get them from?
In my case it was in parsing text where a numeric value had a two character prefix but a string value did not. So I was matching on 0..2 (actually 0..2.min(string.len()) which doubly highlights the indexing issue) which blew up occasionally depending on the string values. There are perhaps smarter ways to do this (e.g. splitn on a space, regex, giant if-else statement, etc, etc) but this seemed at first glance to be the most efficient way because it all fit neatly into a match statement.

The inverse was also a problem: laying out text with a monospace font knowing that every character took up the same number of pixels along the x-axis (e.g. no odd emoji or whatever else). Gotta make sure to call #len on #chars instead of the string itself as some of the text (Windows-1250 encoded) got converted into multi-byte Unicode codepoints.

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