From d3529bfdb41d94a0e6f6ba48e25e4dd4da13eadc Mon Sep 17 00:00:00 2001
From: fhasse95 <49185957+fhasse95@users.noreply.github.com>
Date: Fri, 16 Oct 2026 23:22:27 +0200
Subject: [PATCH] Added support for Dictionary(_:uniquingKeysWith:)

---
 README.md                                |   1 +
 Sources/SkipLib/Dictionary.swift         |   1 -
 Sources/SkipLib/Skip/Dictionary.kt       |  13 +++
 Tests/SkipLibTests/DictionaryTests.swift | 109 +++++++++++++++++++++++
 4 files changed, 123 insertions(+), 1 deletion(-)

diff --git a/README.md b/README.md
index 003e514..3c1b9bf 100644
--- a/README.md
+++ b/README.md
@@ -370,6 +370,7 @@ Support levels:
 <li><code>init()</code></li>
 <li><code>init(minimumCapacity: Int)</code></li>
 <li><code>init(uniqueKeysWithValues keysAndValues: any Sequence&lt;(Key, Value)&gt;)</code></li>
+<li><code>init(_ keysAndValues: any Sequence&lt;(Key, Value)&gt;, uniquingKeysWith combine: (Value, Value) throws -&gt; Value) rethrows</code></li>
 <li><code>func filter(_ isIncluded: ((Key, Value)) throws -&gt; Bool) rethrows -&gt; Dictionary&lt;Key, Value&gt;</code></li>
 <li><code>subscript(key: Key) -&gt; Value?</code></li>
 <li><code>subscript(key: Key, default defaultValue: Value) -&gt; Value</code></li>
diff --git a/Sources/SkipLib/Dictionary.swift b/Sources/SkipLib/Dictionary.swift
index f44865c..2d0f233 100644
--- a/Sources/SkipLib/Dictionary.swift
+++ b/Sources/SkipLib/Dictionary.swift
@@ -23,7 +23,6 @@ public struct Dictionary<Key, Value>: Collection {
     public init(uniqueKeysWithValues keysAndValues: any Sequence<(Key, Value)>) {
     }
 
-    @available(*, unavailable)
     public init(_ keysAndValues: any Sequence<(Key, Value)>, uniquingKeysWith combine: (Value, Value) throws -> Value) rethrows {
     }
 
diff --git a/Sources/SkipLib/Skip/Dictionary.kt b/Sources/SkipLib/Skip/Dictionary.kt
index d0f57da..a5e1238 100644
--- a/Sources/SkipLib/Skip/Dictionary.kt
+++ b/Sources/SkipLib/Skip/Dictionary.kt
@@ -76,6 +76,19 @@ class Dictionary<K, V>: Collection<Tuple2<K, V>>, MutableStruct, KotlinConvertin
         _entryCollection = EntryCollection(this)
     }
 
+    @Suppress("UNCHECKED_CAST")
+    constructor(keysAndValues: Sequence<Tuple2<K, V>>, uniquingKeysWith: (V, V) -> V): this() {
+        for (entry in keysAndValues.iterable) {
+            val key = entry.element0
+            val value = entry.element1
+            if (storage.containsKey(key)) {
+                storage[key] = uniquingKeysWith((storage[key] as V).sref(), value).sref()
+            } else {
+                storage[key] = value
+            }
+        }
+    }
+
     @Suppress("UNCHECKED_CAST")
     constructor(map: Map<K, V>, nocopy: Boolean = false, shared: Boolean = false) {
         if (nocopy && map is LinkedHashMap<*, *>) {
diff --git a/Tests/SkipLibTests/DictionaryTests.swift b/Tests/SkipLibTests/DictionaryTests.swift
index 5cb1265..bc15ab6 100644
--- a/Tests/SkipLibTests/DictionaryTests.swift
+++ b/Tests/SkipLibTests/DictionaryTests.swift
@@ -26,6 +26,108 @@ import Testing
         #expect(multipleElementDictionary["b"] == 2)
     }
 
+    @Test func uniquingKeysInitCombinesInSequenceOrder() {
+        let pairs = [("a", 1), ("b", 2), ("a", 3), ("a", 4)]
+        var combinedValues: [Int] = []
+
+        let result = Dictionary(pairs, uniquingKeysWith: { old, new in
+            combinedValues.append(old)
+            combinedValues.append(new)
+            return old * 10 + new
+        })
+
+        #expect(result == ["a": 134, "b": 2])
+        #expect(combinedValues == [1, 3, 13, 4])
+    }
+
+    @Test func uniquingKeysInitCanKeepFirstOrLastValue() {
+        let pairs = [("a", 1), ("b", 2), ("a", 3)]
+
+        let first = Dictionary(pairs, uniquingKeysWith: { old, _ in old })
+        let last = Dictionary(pairs, uniquingKeysWith: { _, new in new })
+
+        #expect(first == ["a": 1, "b": 2])
+        #expect(last == ["a": 3, "b": 2])
+    }
+
+    @Test func uniquingKeysInitPreservesNilValues() {
+        let pairs: [(String, Int?)] = [("a", nil), ("a", 1), ("a", nil), ("b", nil)]
+        var combinations = 0
+        var sawInitialNil = false
+
+        let result = Dictionary(pairs, uniquingKeysWith: { old, new in
+            if combinations == 0 {
+                sawInitialNil = old == nil
+            }
+            combinations += 1
+            return new
+        })
+
+        #expect(combinations == 2)
+        #expect(sawInitialNil)
+        #expect(result.count == 2)
+        #expect(result.keys.contains("a"))
+        #expect(result.keys.contains("b"))
+        #expect(result.values.allSatisfy { $0 == nil })
+    }
+
+    @Test func uniquingKeysInitDoesNotCombineUniqueOrEmptyInput() {
+        let pairs = [("a", 1), ("b", 2)]
+        let emptyPairs: [(String, Int)] = []
+        var combinations = 0
+        let combine: (Int, Int) -> Int = { _, new in
+            combinations += 1
+            return new
+        }
+
+        let result = Dictionary(pairs, uniquingKeysWith: combine)
+        let empty = Dictionary(emptyPairs, uniquingKeysWith: combine)
+
+        #expect(result == ["a": 1, "b": 2])
+        #expect(empty.isEmpty)
+        #expect(combinations == 0)
+    }
+
+    @Test func uniquingKeysInitPropagatesCombinerError() {
+        let pairs = [("a", 1), ("a", 2), ("a", 3)]
+        var combinations = 0
+        var caughtExpectedError = false
+        let combine: (Int, Int) throws -> Int = { _, _ in
+            combinations += 1
+            throw CombinationError.failed
+        }
+
+        do {
+            _ = try Dictionary(pairs, uniquingKeysWith: combine)
+        } catch {
+            caughtExpectedError = error is CombinationError
+        }
+
+        #expect(caughtExpectedError)
+        #expect(combinations == 1)
+    }
+
+    @Test func uniquingKeysInitPreservesValueSemantics() {
+        var original = [1]
+        let pairs = [("a", original), ("a", [2])]
+        var combined: [Int] = []
+
+        var result = Dictionary(pairs, uniquingKeysWith: { old, new in
+            combined = old + new
+            return combined
+        })
+        original.append(3)
+        combined.append(4)
+        var copy = result
+        copy["a"]?.append(5)
+        result["a"]?.append(6)
+
+        #expect(pairs[0].1 == [1])
+        #expect(result["a"] == [1, 2, 6])
+        #expect(copy["a"] == [1, 2, 5])
+        #expect(combined == [1, 2, 4])
+    }
+
     @Test func subscriptDidSet() {
         let holder = DictionaryHolder()
         holder.dictionary["a"] = 1
@@ -162,3 +264,10 @@ private class DictionaryHolder {
         }
     }
 }
+
+// MARK: - Test Errors
+private extension DictionaryTests {
+    enum CombinationError: Error {
+        case failed
+    }
+}