From 1ccb8b24578040741d873bb0529301f05e48ef97 Mon Sep 17 00:00:00 2001
From: Oliver Booth <me@olivr.me>
Date: Tue, 21 Apr 2020 04:16:46 +0100
Subject: [PATCH] =?UTF-8?q?=E2=9C=A8=20Add=20ReflectionExtensions?=
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- `GetDefaultValue` and `GetDefaultValue<T>` - gets the value stored in
the member's `DefaultValue` attribute
- `GetDescription`- gets the value stored in the member's `Description`
attribute
- `SelectFromCustomAttribute<T1, T2>` - Internally calls
`GetCustomAttribute<T1>` and passes it to a `Func<T1, T2>` so that
specific members may be selected
---
 X10D/src/ReflectionExtensions.cs | 113 +++++++++++++++++++++++++++++++
 1 file changed, 113 insertions(+)
 create mode 100644 X10D/src/ReflectionExtensions.cs

diff --git a/X10D/src/ReflectionExtensions.cs b/X10D/src/ReflectionExtensions.cs
new file mode 100644
index 0000000..25fbc54
--- /dev/null
+++ b/X10D/src/ReflectionExtensions.cs
@@ -0,0 +1,113 @@
+namespace X10D
+{
+    using System;
+    using System.ComponentModel;
+    using System.Reflection;
+
+    /// <summary>
+    /// Extension methods for various reflection types.
+    /// </summary>
+    public static class ReflectionExtensions
+    {
+        /// <summary>
+        /// Gets the value set in this member's annotated <see cref="DefaultValueAttribute"/>, or
+        /// <see langword="default"/> if none exists.
+        /// </summary>
+        /// <param name="member">The member.</param>
+        /// <returns>Returns an <see cref="object"/> representing the value stored in this member's
+        /// <see cref="DefaultValueAttribute"/>.</returns>
+        /// <exception cref="ArgumentNullException"><paramref name="member"/> is <see langword="null"/>.</exception>
+        public static object GetDefaultValue(this MemberInfo member)
+        {
+            if (member is null)
+            {
+                throw new ArgumentNullException(nameof(member));
+            }
+
+            if (!(member.GetCustomAttribute<DefaultValueAttribute>() is { } attribute))
+            {
+                return default;
+            }
+
+            return attribute.Value;
+        }
+
+        /// <summary>
+        /// Gets the value set in this member's annotated <see cref="DefaultValueAttribute"/>, or
+        /// <see langword="default"/> if none exists.
+        /// </summary>
+        /// <typeparam name="T">The type to which the value should cast.</typeparam>
+        /// <param name="member">The member.</param>
+        /// <returns>Returns an instance of <typeparamref name="T"/> representing the value stored in this member's
+        /// <see cref="DefaultValueAttribute"/>.</returns>
+        /// <exception cref="ArgumentNullException"><paramref name="member"/> is <see langword="null"/>.</exception>
+        public static T GetDefaultValue<T>(this MemberInfo member)
+        {
+            if (member is null)
+            {
+                throw new ArgumentNullException(nameof(member));
+            }
+
+            return (T)member.GetDefaultValue();
+        }
+
+        /// <summary>
+        /// Gets the value set in this member's annotated <see cref="DescriptionAttribute"/>, or
+        /// <see langword="null"/> if none exists.
+        /// </summary>
+        /// <param name="member">The member.</param>
+        /// <returns>Returns an instance of <typeparamref name="T"/> representing the value stored in this member's
+        /// <see cref="DescriptionAttribute"/>.</returns>
+        /// <exception cref="ArgumentNullException"><paramref name="member"/> is <see langword="null"/>.</exception>
+        public static string GetDescription(this MemberInfo member)
+        {
+            if (member is null)
+            {
+                throw new ArgumentNullException(nameof(member));
+            }
+
+            if (!(member.GetCustomAttribute<DescriptionAttribute>() is { } attribute))
+            {
+                return null;
+            }
+
+            return attribute.Description;
+        }
+
+        /// <summary>
+        /// Retrieves a custom attribute of a specified type that is applied to the specified member, and passes it
+        /// to a selector delegate in order to select one or more the members in the attribute.
+        /// </summary>
+        /// <typeparam name="TAttribute">The attribute type.</typeparam>
+        /// <typeparam name="TReturn">The return type of the <paramref name="selector"/> delegate.</typeparam>
+        /// <param name="member">The member.</param>
+        /// <param name="selector">The selector delegate.</param>
+        /// <returns>Returns an instance of <typeparamref name="TReturn"/> as provided from
+        /// <paramref name="selector"/>.</returns>
+        /// <exception cref="ArgumentNullException"><paramref name="member"/> is <see langword="null"/>
+        /// -or-
+        /// <paramref name="selector"/> is <see langword="null"/>.</exception>
+        public static TReturn SelectFromCustomAttribute<TAttribute, TReturn>(
+            this MemberInfo member,
+            Func<TAttribute, TReturn> selector)
+            where TAttribute : Attribute
+        {
+            if (member is null)
+            {
+                throw new ArgumentNullException(nameof(member));
+            }
+
+            if (selector is null)
+            {
+                throw new ArgumentNullException(nameof(selector));
+            }
+
+            if (!(member.GetCustomAttribute<TAttribute>() is { } attribute))
+            {
+                return default;
+            }
+
+            return selector(attribute);
+        }
+    }
+}