Why pattern matching matters in C Sharp (C#) - Performance Analysis

Time Complexity: Why pattern matching matters

O(n)

Understanding Time Complexity

When using pattern matching in C#, it is important to understand how it affects the speed of your program.

We want to know how the time to check patterns grows as we add more cases or more complex patterns.

Scenario Under Consideration

Analyze the time complexity of this pattern matching example.

string Describe(object obj) {
    return obj switch {
        int i => $"Integer {i}",
        string s => $"String {s}",
        null => "Null value",
        _ => "Unknown type"
    };
}
    

This code checks the type of an object and returns a description based on the pattern matched.

Identify Repeating Operations

Look at what repeats when matching patterns.

• Primary operation: Checking each pattern case one by one.
• How many times: Up to the number of patterns until one matches.

How Execution Grows With Input

As you add more pattern cases, the program may check more before finding a match.

Number of Patterns (n)	Approx. Checks
3	Up to 3 checks
10	Up to 10 checks
100	Up to 100 checks

Pattern observation: The number of checks grows linearly with the number of patterns.

Final Time Complexity

Time Complexity: O(n)

This means the time to find a matching pattern grows in direct proportion to how many patterns you have.

Common Mistake

[X] Wrong: "Pattern matching always runs in constant time because it looks simple."

[OK] Correct: Each pattern is checked one after another until a match is found, so more patterns mean more checks.

Interview Connect

Understanding how pattern matching scales helps you write efficient code and explain your choices clearly in interviews.

Self-Check

What if we used a dictionary lookup instead of switch pattern matching? How would the time complexity change?