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Preconditions.NET provides convenience static methods to help check that a method or a constructor is invoked with proper parameter or not. In other words it checks the pre-conditions. The goal of this class is to improve readability of code.

Preconditions.NET returns the tested value on success, allowing to check and call a method at the same time.

On failure it always throws an ArgumentException, ArgumentNullException or ArgumentOutOfRangeException.

Preconditions.NET v2.0.0 is a complete rewrite that takes advantage of nullable types, the NotNull attribute and the new .NET 6 CallerArgumentExpression attribute. It is no more mandatory to pass the parameter name being checked.

It also adds new methods (cf. checklist) and remove Check.Zero().

Because Preconditions.NET is only one code file, you can either copy the Check.cs class or include the NuGet package to your project :

PM> Install-Package Preconditions.NET

public class Employee : Person
{
    public Employee(string name, string id) : base(Check.NotNullOrEmpty(name))
    {
        Id = Check.NullableButNotEmpty(id);
    }

    public string Id { get; }
}

• Check.NotNull(object)
• Check.NullableButNotEmpty (string)
• Check.NotNullOrEmpty(string)
• Check.NotNullOrEmpty(IEnumerable)
• Check.HasNoNulls(IEnumerable)
• Check.NotEmpty(Guid)
• Check.FileExists()
• Check.DirectoryExists()
• Check.Positive()
• Check.PositiveOrNull()
• Check.Negative()
• Check.NegativeOrNull()
• Check.NotNegative()
• Check.NotNegativeOrNull()
• Check.True(Func)

Feedback, improvements, ideas are welcomed. Feel free to create new issues at the issues section.