Relational Pattern Matching

🚀 C# Tip — Relational Pattern Matching

Relational pattern matching is one of those C# features that quietly removes noise from your code.

No more long if/else chains.

No more unreadable boundary checks.

Just clear, declarative intent.

🧠 What Is Relational Pattern Matching?

Relational patterns let you compare values using operators directly inside pattern matching:

<  >  <=  >=

They are commonly used with switch expressions and is patterns.

✍️ Before vs After

❌ Traditional if / else

if (age < 18)
    category = "Minor";
else if (age <= 65)
    category = "Adult";
else
    category = "Senior";

✅ Relational pattern matching

var category = age switch
{
    < 18 => "Minor",
    <= 65 => "Adult",
    _ => "Senior"
};

Same logic.

Far more readable.

🎯 Real-World Examples

1️⃣ Input Validation

if (quantity is <= 0)
    throw new ArgumentException("Quantity must be positive");

Clear intent. No magic numbers hidden in conditions.

2️⃣ Pricing & Business Rules

var discount = total switch
{
    < 100 => 0m,
    >= 100 and < 500 => 0.05m,
    >= 500 => 0.10m
};

Perfect for business thresholds and rules engines.

3️⃣ HTTP Status Classification

var category = statusCode switch
{
    >= 200 and < 300 => "Success",
    >= 400 and < 500 => "Client Error",
    >= 500 => "Server Error",
    _ => "Unknown"
};

This reads almost like documentation.

4️⃣ Guard Clauses

if (timeout is < 1 or > 60)
    throw new ArgumentOutOfRangeException(nameof(timeout));

Short, expressive, and impossible to misread.

5️⃣ Feature Flags & Thresholds

bool isEnabled = loadPercentage switch
{
    < 70 => true,
    >= 70 and < 90 => allowLimitedMode,
    _ => false
};

No nested logic. No ambiguity.

🧩 Combine with Logical Patterns

Relational patterns really shine when combined with and / or:

if (score is >= 0 and <= 100)
{
    // valid score
}

This replaces two comparisons with one readable rule.

⚠️ When Not to Use It

• ❌ Overly complex rules
• ❌ Heavy side effects
• ❌ Logic that needs explanation or comments

If it stops reading like English, extract a method.

🧠 Why This Matters

Relational pattern matching:

• Improves readability
• Reduces bugs at boundaries
• Makes intent explicit
• Turns conditions into rules

Clean code is not fewer lines. It’s clearer decisions.

🎯 Final Takeaway

If your code has:

• Ranges
• Thresholds
• Guards
• Categories

You should be using relational pattern matching.

Once you start, if/else chains will feel… old.

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