.NET 8 and C# 12 — Default Lambda Parameters

Default Lambda Parameters it’s a new C# 12 feature which allows you to define a default value for a parameter in lambda expressions. In this article, I present how to use this feature.

For demonstration purposes, I created a console application with .NET 8, and I configured the LangVersion in the .csproj file with the preview value:

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net8.0</TargetFramework>
    <ImplicitUsings>enable</ImplicitUsings>
    <Nullable>enable</Nullable>
    <LangVersion>preview</LangVersion>
  </PropertyGroup>
</Project>

To create a default lambda parameter, the syntax and the rules are the same as adding default values for arguments to any method or local function. To create a lambda with a default parameter value, you only need to specify the value of the parameter, for example:

var lambdaDemo = (string name = "User") => Console.WriteLine($"Hello {name}");

This means that if the lambda is now called, without passing any parameter, the default value will be used:

lambdaDemo();

// Output:
Hello User

When calling the lambda informing a parameter, the default value will then not be used:

lambdaDemo("Gandalf");

// Output:
Hello Gandalf

It’s also possible to retrieve the lambda’s default parameter value. For that, you need to use the property Method, and call the GetParemeters informing the position of the parameter you wanna retrieve (in this example there is only one parameter, so for this reason is the position 0):

lambdaDemo.Method.GetParameters()[0].DefaultValue}

// Output:
User

Conclusion

Default Lambda Parameters it’s a new C# 12 feature that allows you to define default values for parameters on lambda expressions, making it possible now to execute lambda expressions without needing to always inform a parameter value.

This is the link for the project in GitHub: https://github.com/henriquesd/DotNet8Examples

If you like this demo, I kindly ask you to give a ⭐️ in the repository.

Thanks for reading!

What’s new in C# 12 — Microsoft Docs

Input parameters of a lambda expression — Microsoft Docs

Optional and parameter array parameters for lambdas and method groups — Microsoft Docs