Adds StringBuilder implementation

Package.swift

@@ -0,0 +1,33 @@
+// swift-tools-version: 6.0
+
+import PackageDescription
+
+let package = Package(
+	name: "StringBuilder",
+	platforms: [
+		.macOS(.v10_15),
+		.iOS(.v13),
+		.tvOS(.v13),
+		.watchOS(.v6),
+		.macCatalyst(.v13)
+	],
+	products: [
+		.library(
+			name: "StringBuilder",
+			targets: [
+				"StringBuilder"
+			]
+		),
+	],
+	targets: [
+		.target(
+			name: "StringBuilder"
+		),
+		.testTarget(
+			name: "StringBuilderTests",
+			dependencies: [
+				"StringBuilder"
+			]
+		),
+	]
+)

README.md

@@ -1,2 +1,129 @@
 # StringBuilder
- Build strings with resultBuilders
+
+<p align="center">
+    <img src="https://img.shields.io/badge/Swift-orange.svg" alt="Swift" />
+    <a href="https://swift.org/package-manager">
+        <img src="https://img.shields.io/badge/swiftpm-compatible-brightgreen.svg?style=flat" alt="Swift Package Manager" />
+    </a>
+</p>
+
+Welcome to **StringBuilder**, a Swift package for dynamically building strings
+using a `resultBuilder`.
+
+## Usage
+
+### Basic String Building
+To build a basic multi-line string:
+```swift
+String {
+	"Line 1"
+	"Line 2"
+}
+```
+
+Becomes...
+```swift
+"""
+Line 1
+Line 2
+"""
+```
+
+### Custom Separator
+A custom separator can be used to control how the strings are joined:
+```swift
+String(separator: " != ") {
+	"String 1"
+	"String 2"
+}
+```
+
+Becomes...
+```swift
+"String 1 != String 2"
+```
+
+### String Convertible Types
+Any type that conforms to `CustomStringConvertible` can be added to the
+string builder:
+```swift
+String {
+	1234
+	true
+	UUID()
+}
+```
+
+Becomes...
+```swift
+1234
+true
+3D5E76E1-CB1D-4FEF-A5CA-3C67AA08BF47
+```
+
+### Nested String Builders
+String builders can be nested with different separators at each level:
+```swift
+String {
+	"One"
+
+	String(separator: ".") {
+		"Two"
+		"Three"
+	}
+
+	"Four"
+
+	String {
+		String {
+			"Five"
+
+			String(separator: "\n\n") {
+				"Six"
+				"Seven"
+			}
+
+			"Eight"
+		}
+
+		"Nine"
+	}
+
+	"Ten"
+}
+```
+
+Becomes...
+```swift
+One
+Two.Three
+Four
+Five
+Six
+
+Seven
+Eight
+Nine
+Ten
+```
+
+## Installation
+
+StringBuilder is distributed using the [Swift Package Manager](https://swift.org/package-manager). To install it within another Swift package, add it as a dependency within your `Package.swift` manifest:
+
+```swift
+let package = Package(
+    // . . .
+    dependencies: [
+        .package(url: "https://github.com/mattcox/StringBuilder.git", branch: "main")
+    ],
+    // . . .
+)
+```
+
+If you’d like to use StringBuilder within an iOS, macOS, watchOS or tvOS app, then use Xcode’s `File > Add Packages...` menu command to add it to your project.
+
+Import `StringBuilder` wherever you’d like to use it:
+```swift
+import StringBuilder
+```

Sources/StringBuilder/String+StringBuilder.swift

@@ -0,0 +1,40 @@
+//
+//  String+StringBuilder.swift
+//  StringBuilder
+//
+//  Created by Matt Cox on 13/08/2024.
+//  Copyright © 2024 Matt Cox. All rights reserved.
+//
+
+extension String {
+/// Initialize a String from multiple Strings or string convertible types.
+///
+/// A result builder allows the string to be composed from multiple types,
+/// and a separator can be specified to control how the strings are joined
+/// together.
+///
+/// - Parameters:
+///   - separator: The separator to insert between each string. This
+///   defaults to a new line.
+///   - contents: A result builder that will be called to populate the
+///   string.
+///
+/// **Example**
+/// ```swift
+/// String(separator: "\n\n") {
+///     "String"
+///     1234
+///     true
+/// }
+///
+/// // String
+/// //
+/// // 1234
+/// //
+/// // true
+/// ```
+///
+	public init(separator: String = "\n", @StringBuilder _ contents: () -> [String]) {
+		self = contents().joined(separator: separator)
+	}
+}

Sources/StringBuilder/StringBuilder.swift

@@ -0,0 +1,72 @@
+//
+//  StringBuilder.swift
+//  StringBuilder
+//
+//  Created by Matt Cox on 13/08/2024.
+//  Copyright © 2024 Matt Cox. All rights reserved.
+//
+
+@resultBuilder
+public enum StringBuilder {
+	public static func buildBlock() -> String {
+		""
+	}
+}
+
+public extension StringBuilder {
+	static func buildPartialBlock(first: CustomStringConvertible) -> [String] {
+		[first.description]
+	}
+
+	static func buildPartialBlock(accumulated: [String], next: CustomStringConvertible) -> [String] {
+		accumulated + [next.description]
+	}
+
+	static func buildPartialBlock(first: String) -> [String] {
+		[first]
+	}
+
+	static func buildPartialBlock(accumulated: [String], next: String) -> [String] {
+		accumulated + [next]
+	}
+
+	static func buildPartialBlock(first: [String]) -> [String] {
+		first
+	}
+
+	static func buildPartialBlock(accumulated: [String], next: [String]) -> [String] {
+		accumulated + next
+	}
+}
+
+public extension StringBuilder {
+	static func buildOptional(_ component: String?) -> [String] {
+		if let component {
+			return [component]
+		}
+
+		return []
+	}
+
+	static func buildOptional(_ component: [String]?) -> [String] {
+		component ?? []
+	}
+}
+
+public extension StringBuilder {
+	static func buildEither(first component: [String]) -> [String] {
+		component
+	}
+
+	static func buildEither(second component: [String]) -> [String] {
+		component
+	}
+}
+
+public extension StringBuilder {
+	static func buildArray(_ components: [[String]]) -> [String] {
+		components.flatMap {
+			$0
+		}
+	}
+}