C syntax pattern matching [switch expression]

Example

We first define a color enumeration

public enum ColorEnum
    { 
        Red,
        Blue,
        Black,
    }

Let's write a method to get the color RGB value , Here we use Switch expression , The traditional way is :switch Statement in each of its case Generate a value in the block , Such as this

private Color GetColorRgb(ColorEnum colorEnum)
        {
            switch (colorEnum)
            {
                case ColorEnum.Red:
                    return Color.FromArgb(0, 0, 0);
                case ColorEnum.Blue:
                    return Color.FromArgb(0, 0, 0);
                case ColorEnum.Black:
                    return Color.FromArgb(0, 0, 0);
                default:
                    throw new ArgumentException(message: "invalid enum value", paramName: nameof(ColorEnum));
            }
        }

But this makes people feel repetitive Case,break keyword , Makes the code look less concise , therefore C#8.0 With the help of Switch expression , You can use more concise expressions

private Color GetColorRgb(ColorEnum colorEnum)
        {
          return  colorEnum switch
            {
                ColorEnum.Red =>  Color.FromArgb(0, 0, 0),
                ColorEnum.Blue=> Color.FromArgb(0, 0, 0),
                ColorEnum.Black=> Color.FromArgb(0, 0, 0),
                _               => throw new ArgumentException(message: "invalid enum value", paramName: nameof(ColorEnum));
            };

        }

Here are a few grammar improvements ：

• The variable is located in switch Before keywords . The different order makes it visually easy to distinguish switch Expression and switch sentence .• take case and : The element is replaced with =>. It's simpler , More intuitive .• take default Replace the case with _ Abandon yuan .• The body is an expression , It's not a statement . My previous article 【 Do you really understand Lambda Do you 】 Said , If the last sentence is Return In terms of expression , We can Return and {} Remove this keyword and use => Instead of ！

private Color GetColorRgb(ColorEnum colorEnum)
       => colorEnum switch
            {
                ColorEnum.Red => Color.FromArgb(0, 0, 0),
                ColorEnum.Blue => Color.FromArgb(0, 0, 0),
                ColorEnum.Black => Color.FromArgb(0, 0, 0),
                _ => throw new ArgumentException(message: "invalid enum value", paramName: nameof(ColorEnum));
            };

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