C# 14 Interceptors -- Simple Example

Short Summary

Interceptors in C# 14 allow developers to intercept or replace
method calls at compile time.\
This makes it possible to add behaviors such as logging, validation, and
monitoring without modifying the original code.

Unlike traditional approaches that rely on reflection or dynamic
proxies, interceptors work during compilation, which improves
performance and keeps the codebase cleaner.

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Original Service

csharp
public class PaymentService
{
public void ProcessPayment(decimal amount)
{
Console.WriteLine($"Processing payment: {amount}");
}
}


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Interceptor

csharp
using System.Runtime.CompilerServices;

public static class PaymentInterceptor
{
[InterceptsLocation("Program.cs", line: 12, column: 9)]
public static void ProcessPaymentInterceptor(decimal amount)
{
Console.WriteLine("Payment intercepted!");
Console.WriteLine($"Logging payment amount: {amount}");

if (amount > 1000)
{
Console.WriteLine("High value payment detected.");
}
}
}


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Application Code

csharp
var paymentService = new PaymentService();
paymentService.ProcessPayment(1500);


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Example Output

Payment intercepted!
Logging payment amount: 1500
High value payment detected.

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Why Interceptors Matter

Interceptors enable powerful compile-time features such as:

- Automatic logging
- Validation layers
- Telemetry instrumentation
- Performance monitoring
- Framework-level extensions

All without runtime overhead from reflection or dynamic proxies.

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Conclusion

Interceptors move C# toward compile-time metaprogramming, helping
developers build cleaner and faster architectures.