Light.GuardClauses

A lightweight .NET library for expressive guard clauses.

Why Light.GuardClauses?

• 🧰 130+ assertions cover nullability, collections, text, numbers, ranges, dates, URIs, types, streams, and more.
• ⚡ As fast as handwritten guards — most assertions are optimized and benchmarked against equivalent imperative checks using a dedicated BenchmarkDotNet suite.
• 🏷️ Automatic parameter names - with C# 10 and newer, CallerArgumentExpression produces clear exceptions without repetitive nameof calls.
• 🔄 Validation and assignment in one statement works because throwing guards return the successfully validated value.
• 🧩 Custom exception factories let you control exception construction when the built-in exception does not fit your application.
• 🧠 Tooling-aware contracts support Nullable Reference Types for Roslyn, .NET code analysis, and JetBrains annotations.
• 🚀 Flexible deployment spans broad .NET compatibility, Native AOT, and optional single-file source inclusion.

Light.GuardClauses replaces repetitive parameter checks with expressive extension methods:

public class Foo
{
    private readonly IBar _bar;

    public Foo(IBar? bar) => _bar = bar.MustNotBeNull();
}

The guard returns the validated value, so validation and assignment can stay together. Throwing guards start with Must; Boolean checks such as IsNullOrEmpty, IsValidEnumValue, and IsFileExtension can be used in branching logic.

public void SetMovieRating(Guid movieId, int numberOfStars)
{
    movieId.MustNotBeEmpty();
    numberOfStars.MustBeIn(Range.InclusiveBetween(0, 5));

    var movie = _movieRepo.GetById(movieId);
    movie.AddRating(numberOfStars);
}

Custom exception factories let you replace a guard's default exception with one that fits your application. Some factories receive the values involved in the validation:

numberOfStars.MustBeIn(
    Range.InclusiveBetween(0, 5),
    (rating, range) => new InvalidOperationException(
        $"The rating {rating} is outside the allowed {range}."
    )
);

With C# 10 or newer, caller argument expressions automatically capture expressions such as movieId or numberOfStars for the exception parameter name. When using an older compiler, pass the name explicitly:

movieId.MustNotBeEmpty(nameof(movieId));

See the documentation index, assertion overview, and usage guide for more.

Target frameworks

The NuGet package contains three target-framework assets. NuGet automatically selects the best compatible asset for the consuming project:

• .NET Standard 2.0 provides the portable Light.GuardClauses API with the broadest runtime compatibility. It is selected for .NET Framework and other implementations that support .NET Standard 2.0 but not 2.1.
• .NET Standard 2.1 provides the portable Light.GuardClauses API for newer .NET implementations. It is selected for .NET Core 3.0+, .NET 5–9, and other implementations that support .NET Standard 2.1.
• .NET 10 provides the full API for .NET 10 and later, including generic-math overloads, additional span and memory overloads, trimming annotations, framework-optimized implementations, and declared Native AOT compatibility.

Installation

Light.GuardClauses is available from NuGet.

• .NET CLI: dotnet add package Light.GuardClauses
• Package Manager Console: Install-Package Light.GuardClauses
• Project file: <PackageReference Include="Light.GuardClauses" />

To embed the library without a DLL dependency, use the committed .NET Standard 2.0 single-file distribution or create a tailored file with the Light.GuardClauses.SourceCodeTransformation project.

Design and quality

The library supports nullable reference types, .NET code-analysis attributes, JetBrains contract annotations, and Native AOT. Its functional behavior is covered by the test suite, and performance-sensitive assertions can be measured with the current benchmark project.

For the design history behind guard clauses and design by contract, see Guard clause background.

Let there be Light!