Merge pull request #32 from messerli-informatik-ag/individual-or-none

Implement FirstOrNone, LastOrNone and SingleOrNone

Funcky.Test/EnumerableExtensionTest.cs

@@ -1,9 +1,12 @@
-using System.Collections.Generic;
+using System;
+using System.Collections.Generic;
 using System.Linq;
 using Funcky.Extensions;
 using Funcky.Monads;
 using Xunit;
 
+using static Funcky.Functional;
+
 namespace Funcky.Test
 {
     public class EnumerableExtensionTest
@@ -77,25 +80,75 @@ public void WhereSelectFiltersEmptyValues()
             Assert.Equal(expectedResult, result);
         }
 
+        [Theory]
+        [MemberData(nameof(ValueReferenceEnumerables))]
+        public void GivenAnValueEnumerableFirstLastOrNoneGivesTheCorrectOption(List<int> valueEnumerable, List<string> referenceEnumerable)
+        {
+            Assert.Equal(ExpectedOptionValue(valueEnumerable), valueEnumerable.FirstOrNone().Match(false, True));
+            Assert.Equal(ExpectedOptionValue(referenceEnumerable), referenceEnumerable.FirstOrNone().Match(false, True));
+
+            Assert.Equal(ExpectedOptionValue(valueEnumerable), valueEnumerable.LastOrNone().Match(false, True));
+            Assert.Equal(ExpectedOptionValue(referenceEnumerable), referenceEnumerable.LastOrNone().Match(false, True));
+        }
+
+        [Theory]
+        [MemberData(nameof(ValueReferenceEnumerables))]
+        public void GivenAnEnumerableSingleOrNoneGivesTheCorrectOption(List<int> valueEnumerable, List<string> referenceEnumerable)
+        {
+            ExpectedSingleOrNoneBehaviour(valueEnumerable, () => valueEnumerable.SingleOrNone().Match(false, True));
+            ExpectedSingleOrNoneBehaviour(valueEnumerable, () => referenceEnumerable.SingleOrNone().Match(false, True));
+        }
+
+        public static TheoryData<List<int>, List<string>> ValueReferenceEnumerables()
+            => new TheoryData<List<int>, List<string>>
+            {
+                { new List<int>(), new List<string>() },
+                { new List<int> { 1 }, new List<string> { "a" } },
+                { new List<int> { 1, 2, 3 }, new List<string> { "a", "b", "c" } },
+            };
+
         private static Option<int> SquareEvenNumbers(int number)
             => IsEven(number) ? Option.Some(number * number) : Option<int>.None();
 
         private static bool IsEven(int number) => number % 2 == 0;
 
-        private void AcceptIntegers(IEnumerable<int> values)
+        private static void AcceptIntegers(IEnumerable<int> values)
         {
             foreach (var value in values)
             {
                 Assert.Equal(42, value);
             }
         }
 
-        private void AcceptUnits(IEnumerable<Unit> units)
+        private static void AcceptUnits(IEnumerable<Unit> units)
         {
             foreach (var unit in units)
             {
                 Assert.Equal(default, unit);
             }
         }
+
+        private static bool ExpectedOptionValue<T>(List<T> valueEnumerable) =>
+            valueEnumerable.Count switch
+            {
+                0 => false,
+                _ => true,
+            };
+
+        private static void ExpectedSingleOrNoneBehaviour<T>(List<T> list, Func<bool> singleOrNone)
+        {
+            switch (list.Count)
+            {
+                case 0:
+                    Assert.False(singleOrNone());
+                    break;
+                case 1:
+                    Assert.True(singleOrNone());
+                    break;
+                default:
+                    Assert.Throws<InvalidOperationException>(() => singleOrNone());
+                    break;
+            }
+        }
     }
 }

Funcky/Extensions/EnumerableExtensions.cs

@@ -74,5 +74,68 @@ public static void Each<T>(this IEnumerable<T> elements, Action<T> action)
                 action(element);
             }
         }
+
+        /// <summary>
+        /// Returns the first element of a sequence as an <see cref="Option{T}" />, or a <see cref="Option{T}.None" /> value if the sequence contains no elements.
+        /// </summary>
+        /// <typeparam name="TSource">the inner type of the enumerable.</typeparam>
+        public static Option<TSource> FirstOrNone<TSource>(this IEnumerable<TSource> source)
+            where TSource : notnull =>
+            source
+                .Select(Option.Some)
+                .FirstOrDefault();
+
+        /// <summary>
+        /// Returns the first element of the sequence as an <see cref="Option{T}" /> that satisfies a condition or a <see cref="Option{T}.None" /> value if no such element is found.
+        /// </summary>
+        /// <typeparam name="TSource">the inner type of the enumerable.</typeparam>
+        public static Option<TSource> FirstOrNone<TSource>(this IEnumerable<TSource> source, Func<TSource, bool> predicate)
+            where TSource : notnull =>
+            source
+                .Where(predicate)
+                .Select(Option.Some)
+                .FirstOrDefault();
+
+        /// <summary>
+        /// Returns the last element of a sequence as an <see cref="Option{T}" />, or a <see cref="Option{T}.None" /> value if the sequence contains no elements.
+        /// </summary>
+        /// <typeparam name="TSource">the inner type of the enumerable.</typeparam>
+        public static Option<TSource> LastOrNone<TSource>(this IEnumerable<TSource> source)
+            where TSource : notnull =>
+            source
+                .Select(Option.Some)
+                .LastOrDefault();
+
+        /// <summary>
+        /// Returns the last element of a sequence that satisfies a condition as an <see cref="Option{T}" />  or a <see cref="Option{T}.None" /> value if no such element is found.
+        /// </summary>
+        /// <typeparam name="TSource">the inner type of the enumerable.</typeparam>
+        public static Option<TSource> LastOrNone<TSource>(this IEnumerable<TSource> source, Func<TSource, bool> predicate)
+            where TSource : notnull =>
+            source
+                .Where(predicate)
+                .Select(Option.Some)
+                .LastOrDefault();
+
+        /// <summary>
+        /// Returns the only element of a sequence as an <see cref="Option{T}" />, or a <see cref="Option{T}.None" /> value if the sequence is empty; this method throws an exception if there is more than one element in the sequence.
+        /// </summary>
+        /// <typeparam name="TSource">the inner type of the enumerable.</typeparam>
+        public static Option<TSource> SingleOrNone<TSource>(this IEnumerable<TSource> source)
+            where TSource : notnull =>
+            source
+                .Select(Option.Some)
+                .SingleOrDefault();
+
+        /// <summary>
+        /// Returns the only element of a sequence that satisfies a specified condition as an <see cref="Option{T}" /> or a <see cref="Option{T}.None" /> value if no such element exists; this method throws an exception if more than one element satisfies the condition.
+        /// </summary>
+        /// <typeparam name="TSource">the inner type of the enumerable.</typeparam>
+        public static Option<TSource> SingleOrNone<TSource>(this IEnumerable<TSource> source, Func<TSource, bool> predicate)
+            where TSource : notnull =>
+            source
+                .Where(predicate)
+                .Select(Option.Some)
+                .SingleOrDefault();
     }
 }

changelog.md

@@ -9,3 +9,6 @@
 * Add nullability annotations to everything except for `Monads.Reader`.
 * Add a function for creating an `Option<T>` from a nullable value: `Option.From`.
 * `Either.Match` now throws when called on an `Either` value created using `default(Either<L, R>)`.
+* Add `True` and `False` functions to public API
+* Match of `Result` Monad accepts actions
+* Add `FirstOrNone`, `LastOrNone` and `SingleOrNone` extension functions