NSMutableAttributedString is irrational with 𝛑 and 𝒆.

Question

NSMutableAttributedString does strange things with 𝛑 and 𝒆. This is Unicode "Mathematical Bold Small Pi" and the 𝒆 that is near it in the Unicode table. Less exotic characters don't have this problem.

Changing the attribute map of an existing NSMutableAttributedString containing these characters with some foreground colors (like white, for instance) results in a strange doubling of the character when the resulting string is rendered in a CATextLayer. It doesn't happen if the NSMutableAttributedString is created with the different map. It only happens when you use #setAttributes on an existing string.
Displaying an NSMutableAttributedString containing these characters with various colors applied in a UITextField results in the strange doubling regardless of the colors involved. Furthermore, attribute ranges are thrown off by this.

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Hackito Ergo Sum

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It is probably not only irrational, but transcendental 😉. Have a good day.

—
Claude31

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Answer 1

NSMutableAttributedString does strange things with 𝛑 and 𝒆.

Can you post some code snippets showing how you’re doing these mutations?

One thing to note here is that both 𝛑 and 𝒆 are outside of the Basic Multilingual Plane [1], which is tricky when using NSString and friends because they use UTF-16 and hence you have to deal with surrogate pairs. It’s possible that your code is not doing that correctly. Then again, it’s also possible that NSMutableAttributedString is not doing that correctly (-:

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—
Quinn “The Eskimo!” @ Developer Technical Support @ Apple
let myEmail = "eskimo" + "1" + "@" + "apple.com"

[1] Being:

U+1D486 MATHEMATICAL BOLD ITALIC SMALL E
U+1D6D1 MATHEMATICAL BOLD SMALL PI

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eskimo

Looking further into NSMutableAttributedString, I discover that count and length are not the same thing. This affects the attribute boundaries in strange ways. Things start to work when I use length instead of count. The full solution to Problem 2, above, is not as pleasant as I would like, but I can get it to work now. Thanks for pointing me in the right direction.

Problem 1, above, when implemented wrong as I was doing before, still works-or-not depending on the colors used. Weird.

—
Hackito Ergo Sum
And thinking a little further, I find a plausible explanation for the weirdness in Problem 1. Not confirmation-for-sure, but probably not worth pursuing.

—
Hackito Ergo Sum

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Answer 2

NSMutableAttributedString does strange things with 𝛑 and 𝒆.

Can you post some code snippets showing how you’re doing these mutations?

One thing to note here is that both 𝛑 and 𝒆 are outside of the Basic Multilingual Plane [1], which is tricky when using NSString and friends because they use UTF-16 and hence you have to deal with surrogate pairs. It’s possible that your code is not doing that correctly. Then again, it’s also possible that NSMutableAttributedString is not doing that correctly (-:

Share and Enjoy
—
Quinn “The Eskimo!” @ Developer Technical Support @ Apple
let myEmail = "eskimo" + "1" + "@" + "apple.com"

[1] Being:

U+1D486 MATHEMATICAL BOLD ITALIC SMALL E
U+1D6D1 MATHEMATICAL BOLD SMALL PI

Posted by

eskimo

Looking further into NSMutableAttributedString, I discover that count and length are not the same thing. This affects the attribute boundaries in strange ways. Things start to work when I use length instead of count. The full solution to Problem 2, above, is not as pleasant as I would like, but I can get it to work now. Thanks for pointing me in the right direction.

Problem 1, above, when implemented wrong as I was doing before, still works-or-not depending on the colors used. Weird.

—
Hackito Ergo Sum
And thinking a little further, I find a plausible explanation for the weirdness in Problem 1. Not confirmation-for-sure, but probably not worth pursuing.

—
Hackito Ergo Sum

Add a Comment

NSMutableAttributedString is irrational with 𝛑 and 𝒆.

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