Interval Primitives

The descriptor vocabulary for an interval's endpoints — which end (Interval.Bound), whether the endpoint is included (Interval.Boundary), and where a sequence terminates (Interval.Endpoint) — as three small, Foundation-free value types.

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Quick Start

Interval is a namespace of descriptors that specify where an interval begins and ends and how its endpoints behave. It holds the labels only — there is no Interval value type here, no comparison, no arithmetic — so the same vocabulary travels unchanged from the package that constructs ranges through every layer that interprets them.

Each descriptor is a two-case enum forming a Z₂ group: every value has a single opposite, reachable by .opposite or the prefix ! operator.

import Interval_Primitives

// Which end of the interval is this value?
let end: Interval.Bound = .upper
print(end.opposite)        // lower
print(!end)                // lower

// Is the endpoint included in the interval?
let boundary: Interval.Boundary = .closed
print(boundary.isInclusive)   // true
print(boundary.toggled)       // open

// Where does the sequence terminate?
let position: Interval.Endpoint = .start
print(position.opposite)   // end

Each descriptor reads in the vocabulary of its caller. Interval.Bound aliases .lower/.upper as .min/.max and .left/.right; Interval.Endpoint aliases .start/.end as .first/.last and .head/.tail. The underlying case is one value, so a .min produced in one module compares equal to a .lower consumed in another.

To carry a payload alongside a descriptor, each type exposes a Value<Payload> typealias — a Pair of the descriptor and the payload:

import Interval_Primitives
import Pair_Primitives

// Tag a number with the bound it represents.
let labelled: Interval.Bound.Value<Int> = Pair(.lower, 0)
print(labelled.first, labelled.second)   // lower 0

All three descriptors are Sendable, Hashable, CaseIterable, and (outside Embedded) Codable.

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Installation

dependencies: [
    .package(url: "https://github.com/swift-primitives/swift-interval-primitives.git", branch: "main")
]

.target(
    name: "App",
    dependencies: [
        .product(name: "Interval Primitives", package: "swift-interval-primitives"),
    ]
)

Requires Swift 6.3.1 and macOS 26 / iOS 26 / tvOS 26 / watchOS 26 / visionOS 26 (or the matching Linux / Windows toolchain).

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Architecture

The Interval Primitive target is the dependency-free namespace root; each descriptor lives in its own sub-namespace target so a consumer imports only what it uses. The Interval Primitives umbrella re-exports all of them. The Value<Payload> typealiases depend on the Pair primitive.

Product	Target	Purpose
Interval Primitive	Sources/Interval Primitive/	The Interval namespace root. Zero external dependencies.
Interval Bound Primitives	Sources/Interval Bound Primitives/	Interval.Bound — lower/upper endpoint position, with .opposite, aliases (min/max, left/right), and Value<Payload>.
Interval Boundary Primitives	Sources/Interval Boundary Primitives/	Interval.Boundary — closed/open inclusivity, with isInclusive/isExclusive, toggled, and Value<Payload>.
Interval Endpoint Primitives	Sources/Interval Endpoint Primitives/	Interval.Endpoint — start/end sequence position, with .opposite, aliases (first/last, head/tail), and Value<Payload>.
Interval Primitives	Sources/Interval Primitives/	Umbrella re-exporting the namespace and all three descriptor sub-namespaces.
Interval Primitives Test Support	Tests/Support/	Re-exports the umbrella for test consumers.

Foundation-free.

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Platform Support

Platform	Status
macOS 26	Full support
Linux	Full support
Windows	Full support
iOS / tvOS / watchOS / visionOS	Supported

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Community

License

Apache 2.0. See LICENSE.md.