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Merged
merged 5 commits into from
May 14, 2020
Merged

work on char/str descriptions #809

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dcf0963
work on char/str descriptions
RalfJung May 12, 2020
3c6a8f4
fix link
RalfJung May 12, 2020
bd74860
clarify representation
RalfJung May 12, 2020
ed7ad72
tweak str wording
RalfJung May 13, 2020
9af5071
Split str DST into a separate paragraph.
ehuss May 14, 2020
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19 changes: 12 additions & 7 deletions src/types/textual.md
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Expand Up @@ -2,15 +2,20 @@

The types `char` and `str` hold textual data.

A value of type `char` is a [Unicode scalar value] (i.e. a code point that
is not a surrogate), represented as a 32-bit unsigned word in the 0x0000 to
0xD7FF or 0xE000 to 0x10FFFF range. A `[char]` is effectively a UCS-4 / UTF-32
string.
A value of type `char` is a [Unicode scalar value] (i.e. a code point that is
not a surrogate), represented as a 32-bit unsigned word in the 0x0000 to 0xD7FF
or 0xE000 to 0x10FFFF range. It is immediate [Undefined Behavior] to create a
`char` that falls outside this range. A `[char]` is effectively a UCS-4 / UTF-32
string of length 1.

A value of type `str` is a Unicode string, represented as an array of 8-bit
unsigned bytes holding a sequence of UTF-8 code points. Since `str` is a
[dynamically sized type], it is not a _first-class_ type, but can only be
instantiated through a pointer type, such as `&str`.
unsigned bytes holding a sequence of UTF-8 code points. Note that this is a
library-level invariant: for the compiler and core language specification, `str`
is the same as `[u8]`, but methods working on `str` may assume that the data in
there is valid UTF-8 and may cause Undefined Behavior otherwise. Since `str` is
a [dynamically sized type], it can only be instantiated through a pointer type,
such as `&str`.

[Unicode scalar value]: http://www.unicode.org/glossary/#unicode_scalar_value
[Undefined Behavior]: ../behavior-considered-undefined.html
[dynamically sized type]: ../dynamically-sized-types.md