This necessary for ensuring the property that String doesn't keep
inaccessible memory alive. For example, before this change,
String(s.dropFirst().unicodeScalars)
would compile and produce a String that owned inaccessible memory.
Now it no longer compiles.
String's view's SubSequences are the same as the Substring's
view. E.g. String.UnicodeScalarView.SubSequence is
Substring.UnicodeScalarView.
New compatibility inits added, to work around the fact that many
previously failable initializers are now non-failable.
This is a step along the way toward handling backward-compatiblity of UTF8View
slicing and preventing inadvertent creation of String instances that keep
inaccessible memory alive.
I failed to merge the upstream changes to swift-corelibs-foundation at the same
time as I merged that #9806, and it broke on linux. Going to get it right this
time.
As of now:
* old APIs are just marked as `deprecated` not `unavaiable`. To make it
easier to co-operate with other toolchain repos.
* Value variant of API is implemented as public @private
`_ofInstance(_:)`.
This is another necessary step in introducing changes
for SE-0107: UnsafeRawPointer.
UnsafeRawPointer is great for bytewise pointer operations.
OpaquePointer goes away.
The _RawByte type goes away.
StringBuffer always binds memory to the correct CodeUnit
when allocating memory.
Before accessing the string, a dynamic element width check
allows us to assume the bound memory type.
Generic entry points like atomicCompareExchange no longer handle
both kinds of pointers. Normally that's good because you
should not be using generics in that case, just upcast
to raw pointer. However, with pointers-to-pointers
you can't do that.
As proposed by SE-0107: UnsafeRawPointer:
https://github.com/apple/swift-evolution/blob/master/proposals/0107-unsaferawpointer.md#cstring-conversion
Adds String.init(cString: UnsafePointer<UInt8>)
Adds String.nulTerminatedUTF8CString: ContiguousArray<CChar>
This is necessary for eliminating UnsafePointer conversion. Such
conversion is extremely common for interoperability between Swift
strings and C strings to bridge the difference between CChar and
UTF8.CodeUnit. The standard library does not provide any convenient
utilities for converting between the differently typed
buffers. These APIs will handle the simplest cases involving C
interoperability. More convenience can be added later.
In various cases where we had global operators for non-generic
concrete types (such as String + String), move those operators into
the type. This should not affect the sources, but makes the exposition
of the library cleaner.
Plus, it's a good test for the compiler, which uncovered a few issues
where the compiler was coupled with the library.
This documentation revision covers a large number of types & protocols:
String, its views and their indices, the Unicode codec types and protocol,
as well as Character, UnicodeScalar, and StaticString, among others.
This also includes a few small changes across the standard library for
consistency.
