A Swift Package to simplify working with Opaque Collections and Sequences.

When working with a PATs (protocol with assoicatedtype) as an opaque type the assoicatedtype informantion is lost and becomes opaque as well. This means that if you are wanting to reutrn some Sequence or some Collection or some LazySequenceProtocol or some LazyCollectionProtocol the Element type will be lost.

SomeCollection has been created to be able to help make it easy to return the Sequence/Collection PATs as the opaque type without losing what Element is. This is accomplished by providing protocols and conformances to these protocols such as: CollectionOfInt which ensures you are getting a Collection where the Element type is Int. This is essentially the same as if you could say: some Collection<Int>.

Update your Package.swift or Xcode 11+ to include this package as a dependency:

.package(url: "https://github.com/bscothern/SomeCollection.git", from: "1.0.0")

import SomeCollection

func foo() -> some CollectionOfInt {
    [1, 2, 3, 4]
}

print(foo().map({ $0 * 2 }))
// [2, 4, 6, 8]

Here is a list of the common sequence and collection types supported. More are supported but they are less common and not listed here.

• Array
• Set
• Range Types
• Dictionary.Values
• Dictionary.Keys
• Unsafe[Mutable][Raw][Buffer]Pointer
• LazySequence Types

Here is a list the common element types supported. More are supported but they are less common and not listed here.

• Int
• Int8
• Int16
• Int32
• Int64
• UInt
• UInt8
• UInt16
• UInt32
• UInt64
• Double
• Float
• Bool
• Error
• String
• Substring
• Character

SomeCollection has been designed from the start to support custom types. MakeSomeCollectionLib is the engine used to generate the SomeCollection library. It has been setup so users can depend on it to have their own MakeSomeCollectionOfYourOrgName to generate their own additional conformances to Sequence, Collection, or Element types.

You can do this by creating your swift package and having it depend on this package. Create an executable and target along the lines of MakeSomeCollectionOfYourOrgName that makes sense for you and have its target depend on MakeSomeCollectionLib.

It is recommended that your library of generated code be called: SomeCollectionofYourOrgName

You then need to modify the target's main.swift to be similar to this:

import MakeSomeCollectionLib

// YourOrg's Custom Sequences
let sequences: Set<SequenceType> = [
    "CustomSequence1",
    "CustomSequence2",
]

// YourOrg's Custom Collections
let collections: Set<CollectionType> = [
    "CustomCollection1",
    "CustomCollection2",
]

// YourOrg's Elements
let elements: Set<ElementType> = [
    "Element1",
    "Element2",
]

// The matrix of new elements to generate conformances for.
let matrix = GenerationMatrix(
sequenceTypes: sequences.union(StandardLibrarySequenceType.values),
    collectionTypes: collections.union(StandardLibraryCollectionType.values),
    elementTypes: elements.union(StandardLibraryElementType.values)
)

let generator = Generator(matrix: matrix)
try! generator.generate(
    name: "SomeCollectionOfYourOrgLibrary",
    into: "Sources/SomeCollectionOfYourOrg",
    imports: ["YourOrgLibrary"]
)

When doing this it is recommended but not required to have the union() calls with the types defined in MakeSomeCollectionLib. These sets contain all of the types used to generate SomeCollection. By providing the standard library types they will have conformances added to support any new protocols generated through your Element types and your Sequence and Collection types will get conformances to the protocols that already exist in SomeCollection. If the standard library types are provided or not your Sequence and Collection types will get conformances to support the new protocols generated from your Element types.

SeqeunceType, CollectionType, and ElementType all support customization to limit the platforms and/or other types they work with. These can be accessed thorugh calling the initializer directly instead of just specifying the name as a String as shown in the example above. The customization points have been documented so it is easy to work with as you support your own types. If you want a more complex example look at makeTestOutput() in MakeSomeCollectionLibTests.swift which is very similar to what a main.swift would need to be to use MakeSomeCollectionLib.

All generated code is stable in its ordering as long as it is given the same inputs. This helps to cut down on conflicts and identifying what changes.

I have almost certainly missed types and new ones can be added to the standard library each release. In this case you can either open an issue or PR.

• If you open an issue please specify what the type is and I will add support for it if it is in the standard library.
• If you want to submit a PR you will need to update Sources/MakeSomeCollectionLib/StandardLibraryTypes files to know about the new type. Once you have updated the type lists use swift run to have the SomeCollection library rebuild.

I am planning on adding support for Foundation types right away and should have them very soon. They will likely be a part of this same package but in a different library which will likely be named: SomeCollectionOfFoundation.

Open up an issue on github.