fernandostockler / GuardClauses

A collection of extension methods for validating method arguments in order to spot bugs as quickly as possible.

Guard Clauses

Designed to fail early when encountering arguments outside the correct specification.

The bugs I hate are the ones that show up only after hours of successful operation, under unusual circumstances, or whose stack traces lead to dead ends. -Martin Fowler.

Fail fast is a technique that exposes potential bugs early in development, making them immediately visible.

Assertions are the key to failing fast. An assertion is a tiny piece of code that checks a condition and then fails if the condition isn’t met. So, when something starts to go wrong, an assertion detects the problem and makes it visible. -Martin Fowler.

Usage

public enum Category { Client, Vip }

public class Person
{
    int id;
    string name;
    DateOnly birthday;
    Category category;
    double stars;

    public Person(int id, string name, DateOnly birthday, Category category, double stars)
    {
        this.id = Guard.Against.NegativeOrZero(id);

        this.name = Guard.Against.NullOrWhiteSpace(name)
            .And(x => x.Length <= 50, nameof(name))
            .And(x => x.Length >= 3, nameof(name));

        this.birthday = Guard.Against.OutOfRange(birthday,
            minimunValue: new DateOnly(1900, 1, 1),
            maximunValue: new DateOnly(2022, 1, 1));

        this.category = Guard.Against.EnumOutOfRange(category);

        this.stars = Guard.Against.OutOfRange(stars,
            minimunValue: 0,
            maximunValue: 5);
    }
}

Extensions methods

Method	Exception
Guard.Against.Zero	Throw a ArgumentException if the input number is zero.
Guard.Against.Negative	Throw a ArgumentException if the input number is negative.
Guard.Against.NegativeOrZero	Throw a ArgumentException if the input number is negative or zero.
Guard.Against.InvalidRegexFormat	Throw a ArgumentException if the input number does not match with a Regex pattern.
Guard.Against.InvalidInput	Throw a ArgumentException if the input does not pass a predicate function.
Guard.Against.OutOfRange	Throw a ArgumentOutOfRangeException if the input is out of range.
Guard.Against.EnumOutOfRange	Throw a InvalidEnumArgumentException if the input is a not defined enum.
Guard.Against.Null	Throw a ArgumentNullException if the input is null.
Guard.Against.NullOrEmpty	Throw a ArgumentNullException if the input is null or empty.
Guard.Against.NullOrWhiteSpace	Throw a ArgumentNullException if the input is null, empty or white spaces.
And	Throw a ArgumentException if the input does not satisfy a condition.

Custom extensions

You can create your own extension methods by simply extending the IGuardClause interface inside the GuardClauses.Extensions namespace.

namespace GuardClauses.Extensions;

public static class ZipCodeExtensions
{
    public static ZipCode InvalidZipCode(this IGuardClause guardClause, ZipCode zipCode)
        =>  ValidateZipCode(zipCode)
            ? zipCode
            : throw new ArgumentException($"ZipCode ({zipCode}) is invalid.", nameof(zipCode));
}

Usage:

public class Address
{
    string Line1, Line2, City, State, ZipCode;
    
    public Address(string line1, string line2, string city, string state, ZipCode zipCode)
    {
        Line1 = line1;
        ...
        ...
        ZipCode = Guard.Against.InvalidZipCode(zipCode);
    }
    
    ...
}

References

• Addressed by Nick Chapsas on YouTube: How to write clean validation clauses in .NET.
• Inspired by the GitHub project: ardalis/GuardClauses.
• Article: Fail Fast - www.martinfowler.com.