docs/csharp/language-reference/operators/snippets/patterns/LogicalPatterns.cs - main - aprogrammer/dotnet-docs

docs/csharp/language-reference/operators/snippets/patterns/LogicalPatterns.cs

86 строк3 KB

Bill Wagner

Add more details on pattern binding (#43574)

15 ноя 2024, 23:17

15 ноя 2024, 23:17e49964b

namespace Patterns;

public static class LogicalPatterns
{
    public static void Examples()
    {
        AndPattern();
        OrPattern();
    }

    private static void NotPattern(object input)
    {
        // <NotPattern>
        if (input is not null)
        {
            // ...
        }
        // </NotPattern>
    }

    private static void AndPattern()
    {
        // <AndPattern>
        Console.WriteLine(Classify(13));  // output: High
        Console.WriteLine(Classify(-100));  // output: Too low
        Console.WriteLine(Classify(5.7));  // output: Acceptable

        static string Classify(double measurement) => measurement switch
        {
            < -40.0 => "Too low",
            >= -40.0 and < 0 => "Low",
            >= 0 and < 10.0 => "Acceptable",
            >= 10.0 and < 20.0 => "High",
            >= 20.0 => "Too high",
            double.NaN => "Unknown",
        };
        // </AndPattern>
    }

    private static void OrPattern()
    {
        // <OrPattern>
        Console.WriteLine(GetCalendarSeason(new DateTime(2021, 1, 19)));  // output: winter
        Console.WriteLine(GetCalendarSeason(new DateTime(2021, 10, 9)));  // output: autumn
        Console.WriteLine(GetCalendarSeason(new DateTime(2021, 5, 11)));  // output: spring

        static string GetCalendarSeason(DateTime date) => date.Month switch
        {
            3 or 4 or 5 => "spring",
            6 or 7 or 8 => "summer",
            9 or 10 or 11 => "autumn",
            12 or 1 or 2 => "winter",
            _ => throw new ArgumentOutOfRangeException(nameof(date), $"Date with unexpected month: {date.Month}."),
        };
        // </OrPattern>
    }

    // <NegationWithoutParens>
    // Incorrect pattern. `not` binds before `and`
    static bool IsNotLowerCaseLetter(char c) => c is not >= 'a' and <= 'z';
    // </NegationWithoutParens>

    // <DefaultBinding>
    // The default binding without parentheses is shows in this method. `not` binds before `and`
    static bool IsNotLowerCaseLetterDefaultBinding(char c) => c is ((not >= 'a') and <= 'z');
    // </DefaultBinding>

    // <SpecifyBindingOrder>
    // Correct pattern. Force `and` before `not`
    static bool IsNotLowerCaseLetterParentheses(char c) => c is not (>= 'a' and <= 'z');
    // </SpecifyBindingOrder>

    // <WithParentheses>
    static bool IsLetter(char c) => c is (>= 'a' and <= 'z') or (>= 'A' and <= 'Z');
    // </WithParentheses>

    private static void ChangedPrecedence(object input)
    {
        // <ChangedPrecedence>
        if (input is not (float or double))
        {
            return;
        }
        // </ChangedPrecedence>
    }
}