SGuard

SGuard is a lightweight, extensible guard clause library for .NET, providing expressive and robust validation for method arguments, object state, and business rules. It offers both boolean checks (Is.*) and exception-throwing guards (ThrowIf.*), with a unified callback model and rich exception diagnostics.

🚀 Features

• Boolean Guards (Is.*): Check conditions without throwing exceptions.
• Throwing Guards (ThrowIf.*): Throw exceptions when conditions are met, with CallerArgumentExpression-powered messages.
• Any & All Guards: Predicate-based validation for collections.
• Comprehensive Comparison Guards: Between, LessThan, LessThanOrEqual, GreaterThan, GreaterThanOrEqual for generics and strings (with StringComparison).
• Null/Empty Checks: Deep and type-safe null/empty validation for primitives, collections, and complex types.
• Custom Exception Support: Overloads for custom exception types, with constructor argument support.
• Callback Model: Unified SGuardCallback and GuardOutcome for success/failure handling.
• Expression Caching: Efficient, thread-safe caching for compiled expressions.
• Rich Exception Messages: Informative diagnostics using CallerArgumentExpression.
• Multi-targeting: Supports .NET 6, 7, 8, and 9.

📊 Benchmarks

Performance benchmarks for all guard methods are available in the SGuard.Benchmark/benchmarks/ folder. Explore these to see real-world performance comparisons for Is.* and ThrowIf.* methods.

📦 Installation

dotnet add package SGuard

🤔 Why SGuard?

• Clear diagnostics

  • Uses CallerArgumentExpression to produce precise, helpful error messages that point to the exact argument/expression that failed.

• Consistent callback model

  • A single SGuardCallback(outcome) works across both APIs:
    • ThrowIf.* invokes with Failure when it’s about to throw, Success when it passes.
    • Is.* invokes with Success when the result is true, Failure when false.
  • Callback exceptions are safely swallowed, so your validation flow isn’t disrupted.

• Rich exception surface

  • Throw built-in exceptions for common guards or supply your own:
    • Pass a custom exception instance, use a generic TException, or provide constructor arguments for detailed messages.

• Expressive, dual API

  • Choose the style that fits your code:
    • Is.* returns booleans for control-flow friendly checks.
    • ThrowIf.* it fails fast with informative exceptions when rules are violated.

• Culture-aware comparisons and inclusive ranges

  • String overloads accept StringComparison for correct cultural/ordinal semantics.
  • Between checks are inclusive by design for predictable validation.

• Performance and ergonomics

  • Expression caching reduces overhead for repeated checks.
  • Minimal allocations and thread-safe evaluation where applicable.

• Modern .NET support

  • Targets .NET 6, 7, 8, and 9 with multi-targeting, ensuring broad compatibility.

⚡ Quick Start

SGuard helps you validate inputs and state with two complementary APIs:

• ThrowIf.*: fail fast by throwing informative exceptions.
• Is.*: return booleans for control-flow-friendly checks.

1) Validate inputs (fail fast)

public record CreateUserRequest(string Username, int Age, string Email);

public User CreateUser(CreateUserRequest req) 
{ 
    ThrowIf.NullOrEmpty(req);
    ThrowIf.NullOrEmpty(req.Email);
    ThrowIf.NullOrEmpty(req.Username);
    ThrowIf.LessThan(req.Age, 13, new ArgumentException("User must be 13+.", nameof(req.Age)));
    
    // Optionally check formats or ranges
    if (!Is.Between(req.Age, 13, 130))
        throw new ArgumentOutOfRangeException(nameof(req.Age), "Age seems invalid.");

    return new User(req.Username, req.Age, req.Email);
}


public sealed class User 
{ 
    public User(string username, int age, string email) 
    {
        ThrowIf.LessThan(age, 0);
        ThrowIf.NullOrEmpty(email);
        ThrowIf.NullOrEmpty(username);
                
        Age = age;
        Email = email;
        Username = username;
    }
}

2) Check conditions (boolean style)

if (Is.Between(value, min, max)) { /* ... */ }
if (Is.LessThan(a, b)) { /* ... */ }
if (Is.Any(list, x => x > 0)) { /* ... */ }
if (!Is.Between(req.Age, 13, 130))
{
    throw new ArgumentOutOfRangeException(nameof(req.Age), "Age seems invalid.");
}

// Numeric comparisons 
bool inRange = Is.Between(value, min, max); 
bool isLess = Is.LessThan(a, b); 
bool isGreaterOrEqual = Is.GreaterThanOrEqual(a, b);
bool before = Is.LessThan("straße", "strasse", StringComparison.InvariantCulture); // culture-aware

// Collections 
bool anyPositive = Is.Any(numbers, n => n > 0); 
bool allNonNull = Is.All(items, it => it is not null);

// Strings (culture/ordinal aware)
bool lessOrdinal = Is.LessThan("apple", "banana", StringComparison.Ordinal);
bool lessIgnoreCase = Is.LessThan("Apple", "banana", StringComparison.OrdinalIgnoreCase)

3) Callbacks (side effects on success/failure)

// ThrowIf: run side effects on the outcome
ThrowIf.LessThan(1, 2, SGuardCallbacks.OnFailure(() => logger.LogWarning("a < b failed")));
ThrowIf.LessThan(5, 2, SGuardCallbacks.OnSuccess(() => logger.LogInformation("a >= b OK")));

// Is: outcome maps to the boolean result (true=Success, false=Failure)
bool ok = Is.Between(5, 1, 10, SGuardCallbacks.OnSuccess(() => metrics.Increment("is.between.true")));

4) Custom exceptions

ThrowIf.LessThanOrEqual(a, b, new MyCustomException("Invalid!"));
ThrowIf.Between<string, string, string, MyCustomException>(value, min, max, new MyCustomException("Out of range!"));

// Throw using your own exception type
ThrowIf.Any(items, i => i is null, new DomainValidationException("Collection contains null item(s)."));

// Another example with range validation
ThrowIf.LessThanOrEqual(quantity, 0, new DomainValidationException("Quantity must be greater than zero."));

5) String comparisons (culture/ordinal aware)

// Ordinal comparisons
bool before = Is.LessThan("apple", "banana", StringComparison.Ordinal);

// Throw if the ordering violates your rule
ThrowIf.GreaterThan("zebra", "apple", StringComparison.Ordinal); // throws (zebra > apple)

6) Notes

• Between is inclusive (min and max are allowed).
• ThrowIf invokes callbacks with Failure when it’s about to throw, Success when it passes.
• Is.* invokes callbacks with Success when the result is true, Failure when false.
• Callback exceptions are swallowed (they won’t break your validation flow).

Callbacks – When do they run?

• ThrowIf methods:
  • Outcome = Failure → the guard is about to throw (callback runs just before the exception propagates).
  • Outcome = Success → the guard passes (no exception is thrown).
  • If the API fails due to invalid arguments (e.g., null selector or null exception instance), the callback is NOT invoked.

Examples:

// Failure → throws → OnFailure runs
ThrowIf.LessThan(1, 2, SGuardCallbacks.OnFailure(() => logger.LogWarning("a < b failed")));

// Success → no throw → OnSuccess runs
ThrowIf.LessThan(5, 2, SGuardCallbacks.OnSuccess(() => logger.LogInformation("a >= b OK")));

• Is methods:
  • Return a boolean and never throw for the check itself.
  • Outcome = Success when the result is true, Outcome = Failure when the result is false.

Examples

// True → OnSuccess runs
bool inRange = Is.Between(5, 1, 10, SGuardCallbacks.OnSuccess(() => metrics.Increment("is.between.true")));

// False → OnFailure runs
bool isLess = Is.LessThan(5, 2, SGuardCallbacks.OnFailure(() => metrics.Increment("is.lt.false")));

Combine callbacks (Success + Failure)

var onFailure = SGuardCallbacks.OnFailure(() => notifier.Notify("Validation failed"));
var onSuccess = SGuardCallbacks.OnSuccess(() => notifier.Notify("Validation passed"));
SGuardCallback combined = onFailure + onSuccess;

// If inside range -> throws -> Failure -> only onFailure runs
// If outside range -> no throw -> Success -> only onSuccess runs
ThrowIf.Between(value, min, max, combined);

Note: The callback is invoked regardless of the outcome of the guard.

// Passing a null exception instance causes an immediate ArgumentNullException.
// The callback is NOT invoked in this case (no Success/Failure outcome is produced).
try
{
    ThrowIf.Between<int, int, int, InvalidOperationException>(
        5, 1, 10,
        (InvalidOperationException)null!, // invalid argument
        SGuardCallbacks.OnFailure(() => logger.LogError("won't run")));
}
catch (ArgumentNullException)
{
    // expected, and callback not called
}

Inline callback when you need the outcome value directly

GuardOutcome? observed = null;

ThrowIf.LessThan(1, 2, outcome => observed = outcome); // throws -> observed remains null (callback still runs with Failure before exception propagation)

More Examples

Throwing Guards

ThrowIf.NullOrEmpty(str);
ThrowIf.NullOrEmpty(obj, x => x.Property);
ThrowIf.Between(value, min, max); // Throws if value is between min and max
ThrowIf.LessThan(a, b, () => Console.WriteLine("Failed!"));
ThrowIf.Any(list, x => x == null);

// Optionally run a callback on failure (e.g., logging/metrics/cleanup)
ThrowIf.GreaterThan(total, limit, () => logger.LogWarning("Limit exceeded"));

// With selector for nested properties (CallerArgumentExpression helps messages)
ThrowIf.NullOrEmpty(order, o => o.Customer.Name);

📝 Usage Examples (Real-life Scenarios)

public static class CheckoutService 
{ 
    public static void ValidateCart(Cart cart, IReadOnlyDictionary<string, int> stockBySku) 
    { 
        ThrowIf.NullOrEmpty(cart); 
        ThrowIf.NullOrEmpty(cart.Items);
        
        // Every item must have positive quantity
        if (!Is.All(cart.Items, i => i.Quantity > 0))
            throw new ArgumentException("All items must have a positive quantity.", nameof(cart.Items));

        // Check stock levels
        foreach (var item in cart.Items)
        {
            var stock = stockBySku.TryGetValue(item.Sku, out var s) ? s : 0;
            ThrowIf.GreaterThan(item.Quantity, stock, new InvalidOperationException($"Insufficient stock for SKU '{item.Sku}'."));
        }

        // Totals
        ThrowIf.LessThanOrEqual(cart.TotalAmount, 0m, new ArgumentOutOfRangeException(nameof(cart.TotalAmount), "Total must be greater than zero."));
    }
}

public void SaveUser(string username)
{
    var callback = SGuardCallbacks.OnFailure(() =>
        logger.LogWarning("Validation failed: username is required"));

    // When username is null or empty, throw an exception with a custom message and invoke the callback.
    ThrowIf.NullOrEmpty(username, callback);
    
    // Proceed with saving the user...
}

public void UpdateEmail(string email)
{
    var onSuccess = SGuardCallbacks.OnSuccess(() =>
        audit.Record("Email validation succeeded"));

    // If valid, onSuccess is called; if not, an exception is thrown
    ThrowIf.NullOrEmpty(email, onSuccess);

    // Proceed with updating the email...
}

💬 Join the Community Chat

Join our community chat to ask questions, share feedback, or get involved: #sguard:gitter.im

✅ Test and Coverage Status

Test and Coverage Status

Test Results

Total	Passed	Failed	Skipped
367	367	0	0

Code Coverage

Summary

Generated on:	09/05/2025 - 10:39:42
Coverage date:	09/03/2025 - 19:56:53 - 09/05/2025 - 10:39:39
Parser:	MultiReport (12x Cobertura)
Assemblies:	1
Classes:	15
Files:	50
Line coverage:	86.9% (815 of 937)
Covered lines:	815
Uncovered lines:	122
Coverable lines:	937
Total lines:	4360
Branch coverage:	83% (186 of 224)
Covered branches:	186
Total branches:	224
Method coverage:	Feature is only available for sponsors

Name	Covered	Uncovered	Coverable	Total	Line coverage	Covered	Total	Branch coverage
SGuard	815	122	937	4360	86.9%	186	224	83%
SGuard.ExceptionActivator	15	0	15	56	100%	6	8	75%
SGuard.Exceptions.AllException	0	4	4	44	0%	0	0
SGuard.Exceptions.AnyException	2	2	4	36	50%	0	0
SGuard.Exceptions.BetweenException	23	6	29	135	79.3%	0	0
SGuard.Exceptions.GreaterThanException	17	6	23	108	73.9%	0	0
SGuard.Exceptions.GreaterThanOrEqualException	17	6	23	110	73.9%	0	0
SGuard.Exceptions.LessThanException	15	6	21	111	71.4%	0	0
SGuard.Exceptions.LessThanOrEqualException	15	6	21	111	71.4%	0	0
SGuard.Exceptions.NullOrEmptyException	15	4	19	98	78.9%	0	0
SGuard.Is	181	0	181	1100	100%	22	24	91.6%
SGuard.SGuard	31	1	32	124	96.8%	12	12	100%
SGuard.SGuardCallbacks	2	2	4	68	50%	0	0
SGuard.Throw	21	0	21	243	100%	0	0
SGuard.ThrowIf	311	19	330	1558	94.2%	52	56	92.8%
SGuard.Visitor.NullOrEmptyVisitor	150	60	210	458	71.4%	94	124	75.8%

🤝 Contributing

Contributions are welcome! Please see CONTRIBUTING.md for guidelines.

🌐 Code of Conduct

This project adheres to the .NET Foundation Code of Conduct. By participating, you are expected to uphold this code.

📜 License

This project is licensed under the MIT License, a permissive open source license. See the LICENSE file for details.

🔗 Links

• NuGet Package
• Releases