docs/csharp/language-reference/attributes/snippets/NullableAttributes.cs - main - aprogrammer/dotnet-docs

docs/csharp/language-reference/attributes/snippets/NullableAttributes.cs
200 строк5 KB
Bill Wagner
first draft of nameof updates (#29549)
15 июн 2022, 00:43
15 июн 2022, 00:4386ba43a
using System.Diagnostics.CodeAnalysis;

namespace attributes;

#nullable disable
public class NullableOblivious
{
    private Dictionary<string, string> _messageMap = new();
    // <TryGetExample>
    bool TryGetMessage(string key, out string message)
    {
        if (_messageMap.ContainsKey(key))
            message = _messageMap[key];
        else
            message = null;
        return message != null;
    }
    // </TryGetExample>

    // <PropertyExample>
    public string ScreenName
    {
        get => _screenName;
        set => _screenName = value ?? GenerateRandomScreenName();
    }
    private string _screenName;
    // </PropertyExample>
    private static string GenerateRandomScreenName() => throw new NotImplementedException();

    // <MessagingExample>
    public string ReviewComment
    {
        get => _comment;
        set => _comment = value ?? throw new ArgumentNullException(nameof(value), "Cannot set to null");
    }
    string _comment;
    // </MessagingExample>

    // <FindMethod>
    public T Find<T>(IEnumerable<T> sequence, Func<T, bool> predicate)
    // </FindMethod>
    {
        foreach (T item in sequence)
        {
            if (predicate(item)) return item;
        }
        return default;
    }

    // <ThrowWhenNull>
    public static void ThrowWhenNull(object value, string valueExpression = "")
    {
        if (value is null) throw new ArgumentNullException(nameof(value), valueExpression);
    }
    // </ThrowWhenNull>

    // <ExtractComponent>
    string GetTopLevelDomainFromFullUrl(string url)
    // </ExtractComponent>
    {
        return default;
    }

}

#nullable restore
public class NullableAttributes
{
    private Dictionary<string, string> _messageMap = new();

    // <NotNullWhenTryGet>
    bool TryGetMessage(string key, [NotNullWhen(true)] out string? message)
    {
        if (_messageMap.ContainsKey(key))
            message = _messageMap[key];
        else
            message = null;
        return message is not null;
    }
    // </NotNullWhenTryGet>

    // <AllowNullableProperty>
    [AllowNull]
    public string ScreenName
    {
        get => _screenName;
        set => _screenName = value ?? GenerateRandomScreenName();
    }
    private string _screenName = GenerateRandomScreenName();
    // </AllowNullableProperty>
    private static string GenerateRandomScreenName() => throw new NotImplementedException();

    // <DisallowNullProperty>
    [DisallowNull]
    public string? ReviewComment
    {
        get => _comment;
        set => _comment = value ?? throw new ArgumentNullException(nameof(value), "Cannot set to null");
    }
    string? _comment;
    // </DisallowNullProperty>

    // <FindMethodMaybeNull>
    [return: MaybeNull]
    public T Find<T>(IEnumerable<T> sequence, Func<T, bool> predicate)
    // </FindMethodMaybeNull>
    {
        foreach (T item in sequence)
        {
            if (predicate(item)) return item;
        }
        return default;
    }

    // <NotNullThrowHelper>
    public static void ThrowWhenNull([NotNull] object? value, string valueExpression = "")
    {
        _ = value ?? throw new ArgumentNullException(nameof(value), valueExpression);
        // other logic elided
    // </NotNullThrowHelper>
    }

    // <TestThrowHelper>
    public static void LogMessage(string? message)
    {
        ThrowWhenNull(message, $"{nameof(message)} must not be null");

        Console.WriteLine(message.Length);
    }
    // </TestThrowHelper>

    public static void ExampleNullCheck()
    {
        // <NullCheckExample>
        string? userInput = GetUserInput();
        if (!string.IsNullOrEmpty(userInput))
        {
            int messageLength = userInput.Length; // no null check needed.
        }
        // null check needed on userInput here.
        // </NullCheckExample>

    }

    private static string? GetUserInput() => throw new NotImplementedException();

    // <DoesNotReturn>
    [DoesNotReturn]
    private void FailFast()
    {
        throw new InvalidOperationException();
    }

    public void SetState(object containedField)
    {
        if (containedField is null)
        {
            FailFast();
        }

        // containedField can't be null:
        _field = containedField;
    }
    // </DoesNotReturn>

    object _field = new object();

    // <DoesNotReturnIf>
    private void FailFastIf([DoesNotReturnIf(true)] bool isNull)
    {
        if (isNull)
        {
            throw new InvalidOperationException();
        }
    }

    public void SetFieldState(object? containedField)
    {
        FailFastIf(containedField == null);
        // No warning: containedField can't be null here:
        _field = containedField;
    }
    // </DoesNotReturnIf>


    // <ExtractComponentIfNotNull>
    [return: NotNullIfNotNull(nameof(url))]
    string? GetTopLevelDomainFromFullUrl(string? url)
    // </ExtractComponentIfNotNull>
    {
        if (url is null)
        {
            return null;
        }
        else
        {
            return ".com";
        }
    }
}