Static Arrays in Swift

Install as Swift Package

dependencies: [
    .package(url: "github.com/joehinkle11/StaticArray", from: "1.0.0")
]

Usage

import StaticArray

struct MyStruct {
    var normalProperty: Int
    var array1: StaticArray64Bytes<Int> // equivalent `unsigned char data[64]` in C
    var array2: StaticArray64Bytes<Int> // equivalent `unsigned char data[64]` in C
}

var myStruct = MyStruct(
    normalProperty: 1,
    array1: StaticArray64Bytes(), // initialize with all zeros
    array2: StaticArray64Bytes(repeating: 42) // initialize with all 42s
)

print(myStruct.array1[0]) // 0
print(myStruct.array2[0]) // 42
myStruct.array1[0] = 123
print(myStruct.array1[0]) // 123
print(myStruct.array1.count) // 8, because 64 bytes = 8 Ints
print(StaticArray64Bytes<Int>) // 8, because 64 bytes = 8 Ints

Supported Sizes

Static array sizes cannot be chosen arbitrarily. The following sizes are supported:

Size (bytes)	Type
64	`StaticArray64Bytes`
512	`StaticArray512Bytes`
4096	`StaticArray4096Bytes`
32768	`StaticArray32768Bytes`

If you wish to use a different size, you can create a new type which combines several smaller arrays. For example, to create a 128-byte array, you could use two StaticArray64Bytes:

struct StaticArray128Bytes<T> {
    var a: StaticArray64Bytes<T>
    var b: StaticArray64Bytes<T>
}

You can also fork this repository and add support for additional sizes.

How does this work?

Swift can import fixed-size C arrays as tuples. This library is then able to exploit this fact to make fix length arrays in Swift.

Limitations

You cannot use non-PODs (Plain Old Data) types in the array. This means you cannot use classes, strings, or other complex types. You can use simple types like Int, Float, Double, Bool, etc. or even your own structs provided they are don't contain any non-POD types. There is a runtime check to ensure that the type is a POD so you will know if you are trying to use a non-POD type.

References

Thanks to this blog post by ole Begemann for the inspiration: Swift imports fixed-size C arrays as tuples