An extendable guard implementation.

A guard clause helps to check inputs for validity and fails immediately if any invalid inputs are found. The guards are implemented as extension methods on the marker IGuard. This way custom guards can be added to the available default guard clauses.

Check inputs of methods and constructors and fail early. The guard will fail with an exception if the input is not valid.

public void UpdateCustomer(Customer customer)
{
    Guard.Against.Null(customer, nameof(customer));

    // Update the customer...
}

Check inputs constructors, fail early or assign the value. The guard will fail with an exception if the input is not valid or return the input value if it is valid.

public class Customer
{
    public Customer(string name, decimal credit)
    {
        this.Name = Guard.Against.NullOrWhiteSpace(name, nameof(name));
        this.Credit = Guard.Against.Negative(credit, nameof(credit));
    }

    public string Name { get; }

    public decimal Credit { get; }
}

Create your own guards by adding extension methods on IGuard. To create the exception to throw you can use one of the helpers from the ExceptionHelpers class. This helpers make sure that the correct constructors are used and the parameter name is set correctly.

// ReSharper disable once CheckNamespace
namespace Fluxera.Guards
{
    // Note: Using the namespace 'Fluxera.Guard' will ensure that your
    //       custom guard is available throughout your projects.

    using JetBrains.Annotations;
    using static ExceptionHelpers;

    public static class CustomGuardExtensions
    {
        public static void Hello(this IGuard guard, string input, string parameterName, string? message = null)
        {
            if(input.ToLower() == "hello")
            {
                throw CreateArgumentException(parameterName, message);
            }
        }
    }
}

• Guard.Against.Null
  • Throws an ArgumentNullException if the input is null.
• Guard.Against.Default
  • Throws an ArgumentException if the input is default.
• Guard.Against.NullOrEmpty
  • Throws an ArgumentNullException if the input string is null.
  • Throws an ArgumentException if the input string is string.Empty.
  • Throws an ArgumentNullException if the input enumerable is null.
  • Throws an ArgumentException if the input enumerable is empty.
  • Throws an ArgumentNullException if the input nullable guid is null.
  • Throws an ArgumentException if the input nullable guid is Guid.Empty.
• Guard.Against.NullOrWhiteSpace
  • Throws an ArgumentNullException if the input string is null.
  • Throws an ArgumentException if the input string is string.Empty or whitespace-only.
• Guard.Against.Empty
  • Throws an ArgumentException if the input guid is Guid.Empty.
• Guard.Against.Negative
  • Throws an ArgumentException if the input is < 0.
• Guard.Against.Zero
  • Throws an ArgumentException if the input is == 0.
• Guard.Against.NegativeOrZero
  • Throws an ArgumentException if the input is <= 0.
• Guard.Against.OutOfRange
  • Throws an ArgumentOutOfRangeException if the input is not within a given range.
  • Throws an InvalidEnumArgumentException if the input is not a defined enum value.
• Guard.Against.False
  • Throws an ArgumentException if the input is false.
• Guard.Against.True
  • Throws an ArgumentException if the input is true.
• Guard.Against.InvalidInput
  • Throws an ArgumentException if the input doesn't satisfy a predicate.
• Guard.Against.InvalidFormat
  • Throws an ArgumentException if the input doesn't match a regex pattern.