Append TryGetValue to ImmutableHashSet1.Builder and ImmutableSortedSet1.Builder

src/libraries/System.Collections.Immutable/ref/System.Collections.Immutable.cs

@@ -485,6 +485,7 @@ public void IntersectWith(System.Collections.Generic.IEnumerable<T> other) { }
             public bool Remove(T item) { throw null; }
             public bool SetEquals(System.Collections.Generic.IEnumerable<T> other) { throw null; }
             public void SymmetricExceptWith(System.Collections.Generic.IEnumerable<T> other) { }
+            public bool TryGetValue(T equalValue, out T actualValue) { throw null; }
             void System.Collections.Generic.ICollection<T>.Add(T item) { }
             void System.Collections.Generic.ICollection<T>.CopyTo(T[] array, int arrayIndex) { }
             System.Collections.Generic.IEnumerator<T> System.Collections.Generic.IEnumerable<T>.GetEnumerator() { throw null; }
@@ -1021,6 +1022,7 @@ public void IntersectWith(System.Collections.Generic.IEnumerable<T> other) { }
             public System.Collections.Generic.IEnumerable<T> Reverse() { throw null; }
             public bool SetEquals(System.Collections.Generic.IEnumerable<T> other) { throw null; }
             public void SymmetricExceptWith(System.Collections.Generic.IEnumerable<T> other) { }
+            public bool TryGetValue(T equalValue, out T actualValue) { throw null; }
             void System.Collections.Generic.ICollection<T>.Add(T item) { }
             void System.Collections.Generic.ICollection<T>.CopyTo(T[] array, int arrayIndex) { }
             System.Collections.Generic.IEnumerator<T> System.Collections.Generic.IEnumerable<T>.GetEnumerator() { throw null; }

src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableHashSet_1.Builder.cs

@@ -203,6 +203,24 @@ public ImmutableHashSet<T> ToImmutable()
                 return _immutable;
             }
 
+            /// <summary>
+            /// Searches a given value in the set and returns the equal value if it finds
+            /// </summary>
+            /// <param name="equalValue">The value to search.</param>
+            /// <param name="actualValue">The value from the set that the search found, else the original value.</param>
+            /// <returns>A value indicating whether the search was successful.</returns>
+            public bool TryGetValue(T equalValue, out T actualValue)
+            {
+                int hashCode = equalValue != null ? _equalityComparer.GetHashCode(equalValue) : 0;
+                if (_root.TryGetValue(hashCode, out HashBucket bucket))
+                {
+                    return bucket.TryExchange(equalValue, _equalityComparer, out actualValue);
+                }
+
+                actualValue = equalValue;
+                return false;
+            }
+
             #endregion
 
             #region ISet<T> Methods

src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableSortedSet_1.Builder.cs

@@ -458,6 +458,25 @@ public ImmutableSortedSet<T> ToImmutable()
                 return _immutable;
             }
 
+            /// <summary>
+            /// Searches a given value in the set and returns the equal value if it finds
+            /// </summary>
+            /// <param name="equalValue">The value to search.</param>
+            /// <param name="actualValue">The value from the set that the search found, else the original value.</param>
+            /// <returns>A value indicating whether the search was successful.</returns>
+            public bool TryGetValue(T equalValue, out T actualValue)
+            {
+                Node searchResult = _root.Search(equalValue, _comparer);
+                if (!searchResult.IsEmpty)
+                {
+                    actualValue = searchResult.Key;
+                    return true;
+                }
+
+                actualValue = equalValue;
+                return false;
+            }
+
             #region ICollection members
 
             /// <summary>

src/libraries/System.Collections.Immutable/tests/ImmutableHashSetBuilderTest.cs

@@ -332,5 +332,31 @@ public void ToImmutableHashSet()
             ImmutableHashSet<int>.Builder nullBuilder = null;
             AssertExtensions.Throws<ArgumentNullException>("builder", () => nullBuilder.ToImmutableHashSet());
         }
+
+        [Fact]
+        public void TryGetValue()
+        {
+            var builder = ImmutableHashSet.Create(1, 2, 3).ToBuilder();
+            Assert.True(builder.TryGetValue(2, out _));
+
+            builder = ImmutableHashSet.Create(CustomEqualityComparer.Instance, 1, 2, 3, 4).ToBuilder();
+            var existing = 0;
+            Assert.True(builder.TryGetValue(5, out existing));
+            Assert.NotEqual(5, existing);
+            Assert.Equal(4, existing);
+        }
+
+        private class CustomEqualityComparer : IEqualityComparer<int>
+        {
+            private CustomEqualityComparer()
+            {
+            }
+
+            public static CustomEqualityComparer Instance { get; } = new CustomEqualityComparer();
+
+            public bool Equals(int x, int y) => x >> 1 == y >> 1;
+
+            public int GetHashCode(int obj) => (obj >> 1).GetHashCode();
+        }
     }
 }

src/libraries/System.Collections.Immutable/tests/ImmutableSortedSetBuilderTest.cs

@@ -399,5 +399,32 @@ public void ToImmutableSortedSet()
             ImmutableSortedSet<int>.Builder nullBuilder = null;
             AssertExtensions.Throws<ArgumentNullException>("builder", () => nullBuilder.ToImmutableSortedSet());
         }
+
+        [Fact]
+        public void TryGetValue()
+        {
+            var builder = ImmutableSortedSet.Create(1, 2, 3).ToBuilder();
+            Assert.True(builder.TryGetValue(2, out _));
+
+            builder = ImmutableSortedSet.Create(CustomComparer.Instance, 1, 2, 3, 4).ToBuilder();
+            var existing = 0;
+            Assert.True(builder.TryGetValue(5, out existing));
+            Assert.NotEqual(5, existing);
+            Assert.Equal(4, existing);
+        }
+
+        private class CustomComparer : IComparer<int>
+        {
+            private CustomComparer()
+            {
+            }
+
+            public static CustomComparer Instance { get; } = new CustomComparer();
+
+            public int Compare(int x, int y) =>
+                x >> 1 == y >> 1 ? 0 :
+                x < y ? -1 :
+                1;
+        }
     }
 }