Check whether a Unicode code point is assigned

Question

Go has the unicode package, containing useful functions such as IsGraphic or IsPrint. One function that is missing though is IsAssigned. Of course I could write my own function by using the other functions. But I would rather expect the standard library to provide this function. In Java, writing this function is easy:

boolean isAssigned(int codePoint) { return Character.getType(codePoint) != Character.UNASSIGNED; }

In Go there is no function unicode.Type(rune) or unicode.IsAssigned(rune). The closest I could find is this:

func IsAssigned(r rune) bool { return unicode.IsControl(r) || unicode.IsGraphic(r) || unicode.IsSymbol(r) }

But that code thinks that U+00AD (soft-hyphen) is unassigned, which is wrong.

How can I get correct information about unassigned code points?

putu · Accepted Answer · 2018-04-10 23:31:27Z

1

I think you can verify a code point is assigned or not using unicode.Is and unicode.Categories (though it is not efficient), i.e.

func IsAssigned(r rune) bool { for _, v := range unicode.Categories { if unicode.Is(v, r) { return true } } return false }

Working example is in The Go Playground.

answered Apr 10, 2018 at 23:31

putu

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2 Comments

noonex Over a year ago

are you sure that all assigned characters belong to some category? (it is kind of obvious, but maybe you have a quick proof)

noonex Over a year ago

actually code below shows 260+K runes belong to categories, while there is only ~130K codepoints assigned. Do I do something wrong? play.golang.org/p/gIcNVHa5PG6

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