Would you like signs with those chars?

Posted Oct 25, 2022 3:30 UTC (Tue) by tialaramex (subscriber, #21167)
In reply to: Would you like signs with those chars? by joib
Parent article: Would you like signs with those chars?

> Rust also has a 'char' type, which is a 4-byte value capable of storing a single UTF-32 codepoint, presumably under the covers it's considered unsigned.

Rust defines char as a Unicode scalar value, Unicode only has one set of codepoints, and some of them aren't valid scalar values because they were used to make UTF-16 work, but UTF-32 maps all that ones which are scalar values to single code *units* and the rest are invalid.

Thus char::from_u32(0xDE01).unwrap(); will panic because this claims 0xDE01 is a Unicode scalar value, but it isn't because code point U+DE01 is a surrogate used for UTF-16 and has no meaning on its own.

char is not "considered" to be signed or unsigned. You can't do arithmetic on Rust types unless they implement the (Traits signifying) arithmetic operators, which char does not, so in Rust neither 'A' + 'B' nor false + true (bools only implement some logical and bitwise boolean operators, not general arithmetic) work.