Merge pull request #2 from thomaslevesque/getvalueor

Replace GetValueOrDefault with specific extension methods

Author: thomaslevesque

README.md

@@ -46,18 +46,15 @@ Option<int> option = ...
 // Explicit check
 if (option.IsSome)
 {
-    return option.Value;
+    int value = option.Value;
+	...
 }
-else
-{
-    return -1;
-}
-
-// Using GetValueOrDefault
-return option.GetValueOrDefault(-1);
 
 // Using TryGetValue
-return option.TryGetValue(out var value) ? value : -1;
+if (option.TryGetValue(out var value))
+{
+    ...
+}
 ```
 
 ### Usage with Linq

src/Hamlet/NullableAttributes.cs

@@ -0,0 +1,7 @@
+namespace System.Diagnostics.CodeAnalysis
+{
+    /// <summary>Specifies that an output may be null even if the corresponding type disallows it.</summary>
+    [AttributeUsage(AttributeTargets.Field | AttributeTargets.Parameter | AttributeTargets.Property | AttributeTargets.ReturnValue, Inherited = false)]
+    internal sealed class MaybeNullAttribute : Attribute
+    { }
+}

src/Hamlet/Option.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 
 namespace Hamlet
 {
@@ -142,6 +143,49 @@ public static U Match<T, U>(this Option<T> option, Func<T, U> some, Func<U> none
                 : default(T?);
         }
 
+        /// <summary>
+        /// Returns the value of an <see cref="Option{T}"/> if the option is <c>Some</c>, or <c>null</c> if it's <c>None</c>.
+        /// </summary>
+        /// <typeparam name="T">The type of the option's value.</typeparam>
+        /// <param name="option">The option to get the value from.</param>
+        /// <returns>The option's value if it's <c>Some</c>, or <c>null</c> if it's <c>None</c>.</returns>
+        [return: MaybeNull]
+        public static T ValueOrNull<T>(this Option<T> option)
+            where T : class?
+        {
+            return option.IsSome
+                ? option.Value
+                : null;
+        }
+
+        /// <summary>
+        /// Returns the value of an <see cref="Option{T}"/> if the option is <c>Some</c>, or <c>default(T)</c> if it's <c>None</c>.
+        /// </summary>
+        /// <typeparam name="T">The type of the option's value.</typeparam>
+        /// <param name="option">The option to get the value from.</param>
+        /// <returns>The option's value if it's <c>Some</c>, or <c>default(T)</c> if it's <c>None</c>.</returns>
+        public static T ValueOrDefault<T>(this Option<T> option)
+            where T : struct
+        {
+            return option.IsSome
+                ? option.Value
+                : default;
+        }
+
+        /// <summary>
+        /// Returns the value of an <see cref="Option{T}"/> if the option is <c>Some</c>, or <c>defaultValue</c> if it's <c>None</c>.
+        /// </summary>
+        /// <typeparam name="T">The type of the option's value.</typeparam>
+        /// <param name="option">The option to get the value from.</param>
+        /// <param name="defaultValue">The value to return if the option is <c>None</c>.</param>
+        /// <returns>The option's value if it's <c>Some</c>, or <c>defaultValue</c> if it's <c>None</c>.</returns>
+        public static T ValueOr<T>(this Option<T> option, T defaultValue)
+        {
+            return option.IsSome
+                ? option.Value
+                : defaultValue;
+        }
+
         /// <summary>
         /// Converts a <see cref="Nullable{T}"/> to an <see cref="Option{T}"/>, based on whether the nullable has a value.
         /// </summary>

src/Hamlet/OptionOfT.cs

@@ -37,13 +37,6 @@ public Option(T value)
         /// </summary>
         public bool IsNone => !IsSome;
 
-        /// <summary>
-        /// Attempts to get the option's value, if any, or a default value if the option has no value.
-        /// </summary>
-        /// <param name="defaultValue">The default value to return when the option has no value.</param>
-        /// <returns>The option's value, if any, <c>defaultValue</c> otherwise.</returns>
-        public T GetValueOrDefault(T defaultValue = default) => IsSome ? _value : defaultValue;
-
         /// <summary>
         /// Attempts to get the option's value, if any.
         /// </summary>

tests/Hamlet.Tests/OptionOfTTests.cs

@@ -50,27 +50,6 @@ public void Value_throws_for_none()
             exception.Should().BeOfType<InvalidOperationException>();
         }
 
-        [Fact]
-        public void GetValueOrDefault_returns_value_for_some()
-        {
-            var option = Option.Some(42);
-            option.GetValueOrDefault().Should().Be(42);
-        }
-
-        [Fact]
-        public void GetValueOrDefault_returns_default_for_none()
-        {
-            var option = Option.None<int>();
-            option.GetValueOrDefault().Should().Be(0);
-        }
-
-        [Fact]
-        public void GetValueOrDefault_returns_specified_default_for_none()
-        {
-            var option = Option.None<int>();
-            option.GetValueOrDefault(3).Should().Be(3);
-        }
-
         [Fact]
         public void TryGetValue_returns_true_and_sets_value_for_some()
         {

tests/Hamlet.Tests/OptionTests.cs

@@ -151,6 +151,48 @@ public void ToNullable_returns_value_for_some()
             option.ToNullable().Should().Be(42);
         }
 
+        [Fact]
+        public void ValueOrDefault_returns_value_for_some()
+        {
+            var option = Option.Some(42);
+            option.ValueOrDefault().Should().Be(42);
+        }
+
+        [Fact]
+        public void ValueOrDefault_returns_default_for_none()
+        {
+            var option = Option.None<int>();
+            option.ValueOrDefault().Should().Be(0);
+        }
+
+        [Fact]
+        public void ValueOrNull_returns_value_for_some()
+        {
+            var option = Option.Some("hello");
+            option.ValueOrNull().Should().Be("hello");
+        }
+
+        [Fact]
+        public void ValueOrNull_returns_null_for_none()
+        {
+            var option = Option.None<string>();
+            option.ValueOrNull().Should().BeNull();
+        }
+
+        [Fact]
+        public void ValueOr_returns_value_for_some()
+        {
+            var option = Option.Some(42);
+            option.ValueOr(3).Should().Be(42);
+        }
+
+        [Fact]
+        public void ValueOr_returns_default_for_none()
+        {
+            var option = Option.None<int>();
+            option.ValueOr(3).Should().Be(3);
+        }
+
         [Fact]
         public void SomeIfNotNull_nullable_returns_none_for_null()
         {