402 - What's New in Swift

Swift 4

Language refinements and additions

Access control

private can be seen in extensions in the same file.

Composing Classes and Protocols

func shakeEm(controls: [UIControl & Shakeable]) -> array of objects that are UIControl and conform to Shakeable.

Source compatibility

Language hasn't change all that much. Additive features.

Swift 3.2
- Same compiler. Emulates Swift 3, but it's the same compiler.
- Allows Swift 3 syntax that has changed in Swift 4.
3.2 and 4.0 can coexist. Set per-target basis.
- Swift PM understands this too.

Tools and performance

Build Improvements

Preview build system.
Fast, lower overhead, especially in large projects.
Precompiled bridging header, faster compile times.
Shared build for coverage testing
If you want only some functions accessible in ObjC, put them in an @objc extension.
Strip Swift symbols enabled by default. xcrun dyldinfo -export to check symbols.
- Should not be a problem.
Swift standard libraries are stripped as part of app thinning.
- Recommend we leave it enabled.

Standard library

Strings

Unicode Correctness by default.
A character is a grapheme
Equal but differently composed grapheme, cmopare as equal
Strings are collections in Swift 4
Syntax to get to the end of a collection (i...)
Substring type.
- Substrings keep a reference to the original buffer.
- Substrings can share buffer with original string.
- When the string goes out of scope, substring doesn't dissappear.
- Tradeoff -> You need to convert back a Substring to a String, like when assigning to a UILabel.text property.
Multi-line string literals. """ (triple quote to start and end multi-line string literals).
- Indentation of the closing triple quote determines the indentantion each line.

Generics

where closes on associated types, to keep them in sync.

Exclusive access to memory

Compiler checks for access to collections.