SoA

A struct of arrays implementation in pure Swift.

Usage

Add to your package.swift in the dependencies:

.package(url: "https://github.com/jomy10/swift-soa", .branch("master"))

Add to your Package.swift in a target's dependency:

.package(name: "SoA", package: "soa-swift")

New SoA intance

Initialize a Soa instance with an initial capacity of 32 elements.

let soa = SoA(
  Fields()
    .field(Int.self)
    .field(String.self)
)

Changing array capacity

When you want to add more elements than the current capacity of the SoA (soa.capacity), you need to resize it first.

soa.capacity = soa.capacity * 2

Adding elements

When adding elements, you should always make sure you're not adding more elements than the capacity allows.

var soa = SoA(
  Fields().field(Int.self)
)
let idx = 5 // element 5 in array 0 (field 0)
if idx < soa.capacity {
  soa.set(0, at: idx, 69)
} else {
  // resize first
}

Retrieving elements

soa.get(0, at: idx)

Non-primitive types

If you want to add types like classes to the struct of array, you will have to convert them to a pointer first.

For String types, you can use the designated string functions.

soa.get(1, at: 0) as String?
soa.set(1, at: 0, str: "Hello world")

For pointers:

soa.getBufPtr(1, at: 0)
// set pointer and deallocate previous managed pointer at the specified index
soa.set(1, at: 0, ptr: myPtr)
// set pointer, deallocate previous managed pointer at the specified index,
// and add this pointer to be managed by the `SoA`
soa.set(1, at: 0, managedPtr: myPtr)
// set pointer without trying to deallocate the previous pointer
soa.setUnmanaged(1, at: 0, ptr: myPtr)

Strings will always use the soa.set(Int, at: Int, managedPtr: UnsafeRawBufferPointer).

Looping

Using the set method to mutate elements in a loop can be slow, use slice instead.

Primitive types

// Slice field 0
soa.slice(0) { (slice: UnsafeSoASlice<Int>) in
  var slice = slice
  slice[0] = 5
  print(slice[0])
}

Pointers

soa.slice(0) { (slice: UnsafeSoASliceBufPtr<MyType>) in
  var slice = slice
  // set pointer and deallocate previous
  slice[0] = otherPointer
  // set pointer and deallocate previous and manage this one
  slice[managedPtr: 0] = otherPointer
  // set pointer without trying to deallocate
  slice[unmanaged: 0] = otherPointer
  
  print(slice[0])
}

Strings

soa.slice(0) { (slice: UnsafeSoAString) in
  var slice = slice
  slice[0] = "Hello!"
  print(slice[0])
}

Notes

The library is intentionally low-level as it is meant as a "core" library. The user of the library is encouraged to build their own abstraction layer on top of this library.

Running tests

swift test

Running benchmarks

./bench.sh

License

The library is licensed under the GNU LGPL3.0.