Cached lookups for enum [Description] attributes

EnumDescriptions.cs

using System.Collections.Concurrent;

namespace Whatever;

public static class EnumDescriptions
{
    private readonly static ConcurrentDictionary<Type, EnumDescriptionsCache> Cache = new();

    public static IEnumerable<KeyValuePair<Enum, string>> GetValuesAndDescriptions(Type enumType) =>
        GetOrAdd(enumType).GetAll();

    public static IEnumerable<KeyValuePair<TEnum, string>> GetValuesAndDescriptions<TEnum>()
        where TEnum : Enum
    =>
        GetOrAdd(typeof(TEnum))
        .GetAll()
        .Select(x => new KeyValuePair<TEnum, string>((TEnum)x.Key, x.Value));

    public static string GetDescription(Type enumType, Enum value) =>
        GetOrAdd(enumType).GetDescription(value);

    private static EnumDescriptionsCache GetOrAdd(Type enumType)
    {
        return Cache.GetOrAdd(
                    key: enumType ?? throw new ArgumentNullException(nameof(enumType)),
                    valueFactory: x => new EnumDescriptionsCache(x));
    }
}

EnumDescriptionsCache.cs

internal class EnumDescriptionsCache
{
    private readonly Type EnumType;
    private readonly Dictionary<Enum, string> ValueToDescriptionLookup = new();

    public EnumDescriptionsCache(Type enumType)
    {
        EnumType = enumType ?? throw new ArgumentNullException(nameof(enumType));
        if (!EnumType.IsEnum)
            throw new ArgumentException("Must be an Enum type", paramName: nameof(EnumType));

        foreach(Enum enumValue in Enum.GetValues(EnumType))
        {
            FieldInfo fieldInfo = enumValue.GetType().GetField(enumValue.ToString()!)!;
            var descriptionAttribute = fieldInfo.GetCustomAttribute<DescriptionAttribute>();
            string description =
                descriptionAttribute?.Description ?? fieldInfo.Name;
            ValueToDescriptionLookup.Add(enumValue, description);
        }
    }

    public string GetDescription(Enum value) => ValueToDescriptionLookup[value];
    public IEnumerable<KeyValuePair<Enum, string>> GetAll() => ValueToDescriptionLookup;
 }