# Default Parameters in Lambda Expressions

With the release of .NET 10, C# 13 introduces a variety of quality-of-life improvements for developers. One of the standout features is the ability to define **default parameter values in lambda expressions**. This enhancement brings more flexibility and consistency to how we write inline functions.

#### What Changed?

Before C# 13, lambda expressions required all parameters to be explicitly supplied. If you wanted default values, you'd have to wrap your lambda in a method or use null checks and ternary operators inside the lambda body.

With C# 13, you can now define default values directly in the lambda parameter list, just like you can with regular methods.

#### Example

Here’s how it looks in practice:

```csharp
Func<string, string, string> greet = (name = "World", prefix = "Hello") => $"{prefix}, {name}!";

Console.WriteLine(greet()); // Hello, World!
Console.WriteLine(greet("Developer")); // Hello, Developer!
Console.WriteLine(greet("Developer", "Hi")); // Hi, Developer!
```

This makes lambda expressions significantly more concise and expressive, especially when used in callbacks, event handlers, or functional programming patterns.

#### Why It Matters

Adding default parameters to lambdas helps in several ways:

* **Cleaner Code**: Removes the need for wrapper methods or inline null checks.
    
* **More Expressive**: The intent is clearer when default behavior is defined right at the parameter level.
    
* **Useful in Functional Scenarios**: When passing lambdas into LINQ, configuration setups, or task pipelines, it reduces boilerplate.
    

#### Limitations

While this is a powerful feature, there are some caveats to be aware of:

* You must use explicitly-typed lambda expressions. Type inference alone won't work when using default values.
    
* This feature does **not** apply to anonymous methods (`delegate { }`).
    
* It may not be supported by older tooling or analyzers that haven't yet been updated for C# 13.
    

#### Summary

The default parameter values in lambda expressions is a small but impactful improvement in C# 13. It aligns lambdas more closely with traditional methods and opens up new, cleaner ways to write inline logic.

As C# continues to evolve alongside .NET, these kinds of enhancements demonstrate a strong commitment to developer productivity and language consistency.

#### References

* [C# Language Proposal - Default Parameter Values in Lambdas](https://github.com/dotnet/csharplang/issues/2306)
    
* [.NET 10 Preview Release Notes](https://learn.microsoft.com/en-us/dotnet/core/whats-new/dotnet-10)