sharpcompress/src/SharpCompress/NotNullExtensions.cs

using System;
using System.Collections.Generic;
using System.Diagnostics.CodeAnalysis;
using System.Linq;
using System.Runtime.CompilerServices;

namespace SharpCompress;

internal static class NotNullExtensions
{
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public static IEnumerable<T> Empty<T>(this IEnumerable<T>? source) => source ?? [];

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public static IEnumerable<T> Empty<T>(this T? source)
    {
        if (source is null)
        {
            return [];
        }
        return source.AsEnumerable();
    }

#if LEGACY_DOTNET
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public static T NotNull<T>(this T? obj, string? message = null)
        where T : class
    {
        if (obj is null)
        {
            throw new ArgumentNullException(message ?? "Value is null");
        }
        return obj;
    }

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public static T NotNull<T>(this T? obj, string? message = null)
        where T : struct
    {
        if (obj is null)
        {
            throw new ArgumentNullException(message ?? "Value is null");
        }
        return obj.Value;
    }
#else

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public static T NotNull<T>(
        [NotNull] this T? obj,
        [CallerArgumentExpression(nameof(obj))] string? paramName = null
    )
        where T : class
    {
        ArgumentNullException.ThrowIfNull(obj, paramName);
        return obj;
    }

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public static T NotNull<T>(
        [NotNull] this T? obj,
        [CallerArgumentExpression(nameof(obj))] string? paramName = null
    )
        where T : struct
    {
        if (!obj.HasValue)
        {
            throw new ArgumentNullException(paramName);
        }

        return obj.Value;
    }
#endif

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public static string NotNullOrEmpty(this string obj, string name)
    {
        obj.NotNull(name);
        if (obj.Length == 0)
        {
            throw new ArgumentException("String is empty.", name);
        }
        return obj;
    }
}