ReflectionHelper.cs

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// Copyright 2005-2015 Giacomo Stelluti Scala & Contributors. All rights reserved. See License.md in the project root for license information.
 
using System;
using System.Collections.Generic;
using System.Linq;
using System.Reflection;
 
using CommandLine.Core;
 
using CSharpx;
 
namespace CommandLine.Infrastructure
{
    internal static class ReflectionHelper
    {
        [ThreadStatic]
        private static IDictionary<Type, Attribute> _overrides;
 
        public static void SetAttributeOverride(IEnumerable<Attribute> overrides)
        {
            if (overrides != null)
            {
                _overrides = overrides.ToDictionary(attr => attr.GetType(), attr => attr);
            }
            else
            {
                _overrides = null;
            }
        }
 
        public static Maybe<TAttribute> GetAttribute<TAttribute>()
            where TAttribute : Attribute
        {
            // Test support
            if (_overrides != null)
            {
                return
                    _overrides.ContainsKey(typeof(TAttribute))
                        ? Maybe.Just((TAttribute)_overrides[typeof(TAttribute)])
                        : Maybe.Nothing<TAttribute>();
            }
 
            Assembly assembly = GetExecutingOrEntryAssembly();
 
#if NET40
            object[] attributes = assembly.GetCustomAttributes(typeof(TAttribute), false);
#else
            TAttribute[] attributes = assembly.GetCustomAttributes<TAttribute>()
                                              .ToArray();
#endif
 
            return attributes.Length > 0
                       ? Maybe.Just((TAttribute)attributes[0])
                       : Maybe.Nothing<TAttribute>();
        }
 
        public static string GetAssemblyName()
        {
            Assembly assembly = GetExecutingOrEntryAssembly();
 
            return assembly.GetName()
                           .Name;
        }
 
        public static string GetAssemblyVersion()
        {
            Assembly assembly = GetExecutingOrEntryAssembly();
 
            return assembly.GetName()
                           .Version.ToStringInvariant();
        }
 
        public static bool IsFSharpOptionType(Type type)
        {
            return type.FullName.StartsWith("Microsoft.FSharp.Core.FSharpOption`1",
                                            StringComparison.Ordinal
                                           );
        }
 
        public static T CreateDefaultImmutableInstance<T>(Type[] constructorTypes)
        {
            Type t = typeof(T);
 
            return (T)CreateDefaultImmutableInstance(t, constructorTypes);
        }
 
        public static object CreateDefaultImmutableInstance(Type type, Type[] constructorTypes)
        {
            ConstructorInfo ctor = type.GetTypeInfo()
                                       .GetConstructor(constructorTypes);
 
            if (ctor == null)
            {
                throw new
                    InvalidOperationException($"Type {type.FullName} appears to be immutable, but no constructor found to accept values."
                                             );
            }
 
            object[] values = (from prms in ctor.GetParameters()
                               select prms.ParameterType.CreateDefaultForImmutable()).ToArray();
 
            return ctor.Invoke(values);
        }
 
        private static Assembly GetExecutingOrEntryAssembly()
        {
            //resolve issues of null EntryAssembly in Xunit Test #392,424,389
            //return Assembly.GetEntryAssembly();
            return Assembly.GetEntryAssembly() ?? Assembly.GetCallingAssembly();
        }
 
        public static IEnumerable<string> GetNamesOfEnum(Type t)
        {
            if (t.IsEnum)
            {
                return Enum.GetNames(t);
            }
 
            Type u = Nullable.GetUnderlyingType(t);
 
            if (u != null && u.IsEnum)
            {
                return Enum.GetNames(u);
            }
 
            return Enumerable.Empty<string>();
        }
    }
}