@@ 0,0 1,70 @@
+---
+title: "Detecting the Empty Character in Go"
+date: 2020-07-28
+---
+
+Recently, I have been working on an online ticketing system. I have been using
+`strings.TrimSpace` for a while, and it worked well. I tested
+it with the "empty character" from
+[emptycharacter.com](https://emptycharacter.com/), and it failed to detect
+whatever whitespace characters it was using.
+
+I thought it was just `strings.TrimSpace` not detecting different types of
+Unicode's empty characters. So I replaced it with
+`strings.TrimFunc(s, unicode.IsSpace)`, and it still didn't clear the
+spaces[^2].
+
+Disecting that empty character, we find it actually made up of five different
+characters:
+
+- `U+200F`: Right-To-Left Mark
+- `U+200F`: Right-To-Left Mark
+- `U+200E`: Left-To-Right Mark
+- `U+0020`: Regular Space
+- `U+200E`: Left-To-Right Mark
+
+We can see that it is using a control character to prevent the regular space
+from being trimmed.
+
+However, Go doesn't list these characters as control characters[^1], so we
+cannot use `unicode.IsControl`. But it is included in the
+`unicode.Bidi_Control` subset. Here's my first solution:
+
+```go
+func isImproperChar(r rune) bool {
+	return unicode.IsSpace(r) || unicode.In(r, unicode.Bidi_Control)
+}
+
+strings.TrimFunc(s, IsImproperChar)
+```
+
+This would trim away at bi-directional control characters, which is probably
+a really bad idea especially in systems supporting Arabic, Hebrew, or other
+right-to-left languages.
+
+So we can just trim it to measure the length, then discarding the trimmed
+result.
+
+```go
+func IsEmpty(s string) bool {
+	return len(strings.TrimFunc(s, func(r rune) bool {
+		return unicode.IsSpace(r) || unicode.In(r, unicode.Bidi_Control)
+	})) == 0
+}
+```
+
+Try it out on [the Go playground](https://play.golang.org/p/S74NV_KP0Xv)!
+
+Have a better solution? Please let me know!
+
+
+*This is my eighth post in the [#100DaysToOffload](https://100daystooffload.com)
+challenge.*
+
+[^1]: Not listed on
+[unicode/tables.go:7108](https://golang.org/src/unicode/tables.go#L7108) as
+`pC` (control character), but rather it's included in the
+[Bidi_Control](https://golang.org/src/unicode/tables.go#L5673) subset.
+[^2]: I thought `unicode.IsSpace` wasn't detecting detecting some types of
+spaces. But after [some testing](https://play.golang.org/p/S6T9gK5f8lw), that
+doesn't seem to be the case.