CollectionExtensions.cs

// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

using System.Collections.ObjectModel;
using System.Diagnostics.CodeAnalysis;

namespace System.Collections.Generic
{
    public static class CollectionExtensions
    {
        public static TValue? GetValueOrDefault<TKey, TValue>(this IReadOnlyDictionary<TKey, TValue> dictionary, TKey key)
        {
            return dictionary.GetValueOrDefault(key, default!);
        }

        public static TValue GetValueOrDefault<TKey, TValue>(this IReadOnlyDictionary<TKey, TValue> dictionary, TKey key, TValue defaultValue)
        {
            ArgumentNullException.ThrowIfNull(dictionary);

            TValue? value;
            return dictionary.TryGetValue(key, out value) ? value : defaultValue;
        }

        public static bool TryAdd<TKey, TValue>(this IDictionary<TKey, TValue> dictionary, TKey key, TValue value)
        {
            ArgumentNullException.ThrowIfNull(dictionary);

            if (!dictionary.ContainsKey(key))
            {
                dictionary.Add(key, value);
                return true;
            }

            return false;
        }

        public static bool Remove<TKey, TValue>(this IDictionary<TKey, TValue> dictionary, TKey key, [MaybeNullWhen(false)] out TValue value)
        {
            ArgumentNullException.ThrowIfNull(dictionary);

            if (dictionary.TryGetValue(key, out value))
            {
                dictionary.Remove(key);
                return true;
            }

            value = default;
            return false;
        }

        /// <summary>
        /// Returns a read-only <see cref="ReadOnlyCollection{T}"/> wrapper
        /// for the specified list.
        /// </summary>
        /// <typeparam name="T">The type of elements in the collection.</typeparam>
        /// <param name="list">The list to wrap.</param>
        /// <returns>An object that acts as a read-only wrapper around the current <see cref="IList{T}"/>.</returns>
        /// <exception cref="ArgumentNullException"><paramref name="list"/> is null.</exception>
        public static ReadOnlyCollection<T> AsReadOnly<T>(this IList<T> list)
        {
            return new ReadOnlyCollection<T>(list);
        }

        /// <summary>
        /// Returns a read-only <see cref="ReadOnlyDictionary{TKey, TValue}"/> wrapper
        /// for the current dictionary.
        /// </summary>
        /// <typeparam name="TKey">The type of keys in the dictionary.</typeparam>
        /// <typeparam name="TValue">The type of values in the dictionary.</typeparam>
        /// <param name="dictionary">The dictionary to wrap.</param>
        /// <returns>An object that acts as a read-only wrapper around the current <see cref="IDictionary{TKey, TValue}"/>.</returns>
        /// <exception cref="ArgumentNullException"><paramref name="dictionary"/> is null.</exception>
        public static ReadOnlyDictionary<TKey, TValue> AsReadOnly<TKey, TValue>(this IDictionary<TKey, TValue> dictionary) where TKey : notnull
        {
            return new ReadOnlyDictionary<TKey, TValue>(dictionary);
        }
    }
}