The Law
Atomics are hard
Swift 5 turns on exclusivity checking by default. This has some interesting interactions with atomics, especially when running under the Thread Sanitizer (TSAN). If you've ever seen a TSAN report on some simple Swift code that looks obviously correct then you're probably running into this issue:
// Incorrect! Do not use this!
. . .Take Delight in Small Joys
Extensions everywhere
This is a small post about a small joy. I really enjoy how natural extensions can feel in Swift.
I consider it quite unfortunate that UnsafeMutableRawBufferPointer.baseAddress is optional. It makes that type so ugly to use in practice. I also dislike having to specify alignment on allocation; a sensible default is Int.bitWidth / 8 on . . .
Fixed-sized Arrays
Who doesn't like a tuple with 1024 elements?
Let's say we want to statfs() a mount point to determine which BSD device name it belongs to. In english, that means discover that /Volumes/MyDisk comes from /dev/disk6s2.
struct statfs fsinfo;
if (statfs(path, &fsinfo) != 0) {
//error
}
The equivalent Swift code, along with a POSIX error helper:
func . . .SingleValueCodable
A simple exercise in leverage
The new Codable protocol is flexible enough to allow a different encoded representation from the in-memory representation which is a nice property to have in a serialization mechanism. Today I'm going to build SingleValueCodable to automate that work when dealing with RawRepresentable types.
The Setup
I want to encode . . .
AMD System V ABI Reference
An ABI reference for quick lookup. If you crash or just want to step through disassembly, check the contents of the registers to see where parameters are being passed.
| Arg | Register | Notes |
|---|---|---|
| 1 | RDI |
Usually self or address to hold return value |
| 2 | RSI |
Usually _cmd but may . . . |
MemoryLayout
Size & Stride
A quick word of warning to those of you using UnsafePointer and MemoryLayout.
- The
sizeof a type tells you how many bytes it takes to hold that type in memory. - The
strideof a type tells you how far apart each instance of the type is in memory.
If you are doing pointer arithmetic on UnsafePointer then Swift . . .
Swift REPL Targets
Have you seen the message error: repl.swift:2:31: error: '<type>' is only available on OS X <version> or newer? In current releases of Xcode, the Swift REPL uses a hard-coded 10.9 target instead of the current OS.
The solution is fairly easy:
xcrun swift -target x86_64-apple-macosx10.12
. . .