Textual types
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. 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 represented the same way as [u8]
, a slice of
8-bit unsigned bytes. However, the Rust standard library makes extra assumptions
about str
: methods working on str
assume and ensure that the data in there
is valid UTF-8. Calling a str
method with a non-UTF-8 buffer can cause
Undefined Behavior now or in the future.
Since str
is a dynamically sized type, it can only be instantiated through a
pointer type, such as &str
.
Layout and bit validity
char
is guaranteed to have the same size and alignment as u32
on all platforms.
Every byte of a char
is guaranteed to be initialized (in other words,
transmute::<char, [u8; size_of::<char>()]>(...)
is always sound -- but since
some bit patterns are invalid char
s, the inverse is not always sound).