C#  

All you need to know about switch expression and Modern Pattern Matching

The switch statement has been part of C# since day one.

But over time, it has evolved into a powerful tool for pattern matching .

In this article, we'll look at how the switch statement has changed and see why the modern switch is more useful.

The Traditional switch

  • The classic switch has been around since C# 1.0.

  • It only worked on constants (int, char, enums, strings).

  • Each case needed a break (or return).

Example

  
    public string GetColor(Color c)
{
    switch (c)
    {
        case Color.Red:
        case Color.Blue:
        case Color.Yellow:
            return "Primary Colors";

        default:
            return "Other";
    }
}

Modern switch with Pattern Matching

Starting with C# 7.0, the switch statement gained pattern matching. Later releases expanded it:

  • Type patterns, constant patterns, and when clauses.

  • Switch expressions + property/tuple patterns.

  • Relational (>, <, >=, <=) and logical (and, or, not) patterns.

Type patterns Example

  
    object value = 42;

string result = value switch
{
    int n => $"Integer: {n}",
    string s => $"String: {s}",
    null => "Null value",
    _ => "Unknown type"
};

Relational Patterns

This switch expression is used to compare an expression result with a constant, as the following example shows:

  
    int score = 85;

string grade = score switch
{
    >= 90 => "A",
    >= 80 => "B",
    >= 70 => "C",
    >= 60 => "D",
    _ => "F"
};

In a relational pattern, we can use the relational operators <, >, <=, or >=.

Positional pattern

Can be used to deconstruct a result and match it values as the following example:

  
    (int x, int y) point = (5, -3);

string position = point switch
{
    (0, 0) => "Origin",
    ( > 0, > 0) => "Quadrant I",
    ( < 0, > 0) => "Quadrant II",
    ( < 0, < 0) => "Quadrant III",
    ( > 0, < 0) => "Quadrant IV",
    _ => "On axis"
};

There still exists many other patterns present in the documentation, each can be served and used in a specific situation, more specific than the general cases we encounter.

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