MustHaveMaximumLength for immutable array

Code/Light.GuardClauses.Tests/CollectionAssertions/MustHaveLengthInTests.cs

@@ -68,4 +68,47 @@ public static void CallerArgumentExpression()
         act.Should().Throw<ArgumentOutOfRangeException>()
            .WithParameterName(nameof(testArray));
     }
+
+    [Fact]
+    public static void DefaultImmutableArrayInRange()
+    {
+        var defaultArray = default(ImmutableArray<int>);
+
+        var result = defaultArray.MustHaveLengthIn(Range.FromInclusive(0).ToInclusive(5));
+
+        result.IsDefault.Should().BeTrue();
+    }
+
+    [Fact]
+    public static void DefaultImmutableArrayNotInRange()
+    {
+        var defaultArray = default(ImmutableArray<int>);
+
+        var act = () => defaultArray.MustHaveLengthIn(Range.FromInclusive(1).ToInclusive(5), nameof(defaultArray));
+
+        act.Should().Throw<ArgumentOutOfRangeException>()
+           .And.Message.Should().Contain("must have its length in between 1 (inclusive) and 5 (inclusive)")
+           .And.Contain("has no length because it is the default instance");
+    }
+
+    [Fact]
+    public static void DefaultImmutableArrayCustomException()
+    {
+        var defaultArray = default(ImmutableArray<int>);
+
+        Test.CustomException(
+            defaultArray,
+            Range.FromInclusive(1).ToInclusive(5),
+            (array, r, exceptionFactory) => array.MustHaveLengthIn(r, exceptionFactory)
+        );
+    }
+
+    [Fact]
+    public static void DefaultImmutableArrayCustomMessage() =>
+        Test.CustomMessage<ArgumentOutOfRangeException>(
+            message => default(ImmutableArray<int>).MustHaveLengthIn(
+                Range.FromInclusive(1).ToInclusive(5),
+                message: message
+            )
+        );
 }

Code/Light.GuardClauses.Tests/CollectionAssertions/MustHaveMaximumLengthTests.cs

@@ -0,0 +1,90 @@
+using System;
+using System.Collections.Immutable;
+using FluentAssertions;
+using Light.GuardClauses.Exceptions;
+using Xunit;
+
+namespace Light.GuardClauses.Tests.CollectionAssertions;
+
+public static class MustHaveMaximumLengthTests
+{
+    [Theory]
+    [InlineData(new[] { 1, 2, 3, 4 }, 3)]
+    [InlineData(new[] { 1, 2 }, 1)]
+    [InlineData(new[] { 500 }, 0)]
+    public static void ImmutableArrayMoreItems(int[] items, int length)
+    {
+        var immutableArray = items.ToImmutableArray();
+        Action act = () => immutableArray.MustHaveMaximumLength(length, nameof(immutableArray));
+
+        var assertion = act.Should().Throw<InvalidCollectionCountException>().Which;
+        assertion.Message.Should().Contain(
+            $"{nameof(immutableArray)} must have at most count {length}, but it actually has count {immutableArray.Length}."
+        );
+        assertion.ParamName.Should().BeSameAs(nameof(immutableArray));
+    }
+
+    [Theory]
+    [InlineData(new[] { "Foo" }, 1)]
+    [InlineData(new[] { "Bar" }, 2)]
+    [InlineData(new[] { "Baz", "Qux", "Quux" }, 5)]
+    public static void ImmutableArrayLessOrEqualItems(string[] items, int length)
+    {
+        var immutableArray = items.ToImmutableArray();
+        var result = immutableArray.MustHaveMaximumLength(length);
+        result.Should().Equal(immutableArray);
+    }
+
+    [Fact]
+    public static void ImmutableArrayEmpty()
+    {
+        var emptyArray = ImmutableArray<int>.Empty;
+        var result = emptyArray.MustHaveMaximumLength(5);
+        result.Should().Equal(emptyArray);
+    }
+
+    [Theory]
+    [InlineData(new[] { 87, 89, 99 }, 1)]
+    [InlineData(new[] { 1, 2, 3 }, -30)]
+    public static void ImmutableArrayCustomException(int[] items, int maximumLength)
+    {
+        var immutableArray = items.ToImmutableArray();
+
+        Action act = () => immutableArray.MustHaveMaximumLength(
+            maximumLength,
+            (array, length) => new ($"Custom exception for array with length {array.Length} and max {length}")
+        );
+
+        act.Should().Throw<Exception>()
+           .WithMessage($"Custom exception for array with length {immutableArray.Length} and max {maximumLength}");
+    }
+
+    [Fact]
+    public static void ImmutableArrayNoCustomExceptionThrown()
+    {
+        var immutableArray = new[] { "Foo", "Bar" }.ToImmutableArray();
+        var result = immutableArray.MustHaveMaximumLength(2, (_, _) => new ());
+        result.Should().Equal(immutableArray);
+    }
+
+    [Fact]
+    public static void ImmutableArrayCustomMessage()
+    {
+        var immutableArray = new[] { 1, 2, 3 }.ToImmutableArray();
+
+        Test.CustomMessage<InvalidCollectionCountException>(
+            message => immutableArray.MustHaveMaximumLength(2, message: message)
+        );
+    }
+
+    [Fact]
+    public static void ImmutableArrayCallerArgumentExpression()
+    {
+        var myImmutableArray = new[] { 1, 2, 3 }.ToImmutableArray();
+
+        var act = () => myImmutableArray.MustHaveMaximumLength(2);
+
+        act.Should().Throw<InvalidCollectionCountException>()
+           .WithParameterName(nameof(myImmutableArray));
+    }
+}

Code/Light.GuardClauses.Tests/CollectionAssertions/MustNotContainTests.cs

@@ -140,4 +140,51 @@ public static void ImmutableArrayCallerArgumentExpression()
         act.Should().Throw<ExistingItemException>()
            .WithParameterName(nameof(array));
     }
+
+    [Fact]
+    public static void ImmutableArrayDefaultInstanceDoesNotContainItem()
+    {
+        var defaultArray = default(ImmutableArray<int>);
+
+        // Default instance should not throw for any item since it cannot contain anything
+        var result = defaultArray.MustNotContain(42);
+
+        result.IsDefault.Should().BeTrue();
+    }
+
+    [Fact]
+    public static void ImmutableArrayDefaultInstanceCustomException()
+    {
+        var defaultArray = default(ImmutableArray<string>);
+
+        // Default instance should not throw even with custom exception factory
+        var result = defaultArray.MustNotContain(
+            "test",
+            (_, _) => new InvalidOperationException("Should not be called")
+        );
+
+        result.IsDefault.Should().BeTrue();
+    }
+
+    [Fact]
+    public static void ImmutableArrayDefaultInstanceCustomMessage()
+    {
+        var defaultArray = default(ImmutableArray<object>);
+
+        // Default instance should not throw even with custom message
+        var result = defaultArray.MustNotContain(new object(), message: "Custom message");
+
+        result.IsDefault.Should().BeTrue();
+    }
+
+    [Fact]
+    public static void ImmutableArrayDefaultInstanceCallerArgumentExpression()
+    {
+        var defaultArray = default(ImmutableArray<char>);
+
+        // Default instance should not throw, so no exception to check parameter name
+        var result = defaultArray.MustNotContain('x');
+
+        result.IsDefault.Should().BeTrue();
+    }
 }

Code/Light.GuardClauses/Check.MustHaveLengthIn.cs

@@ -75,7 +75,8 @@ public static ImmutableArray<T> MustHaveLengthIn<T>(
         string? message = null
     )
     {
-        if (!range.IsValueWithinRange(parameter.Length))
+        var length = parameter.IsDefault ? 0 : parameter.Length;
+        if (!range.IsValueWithinRange(length))
         {
             Throw.ImmutableArrayLengthNotInRange(parameter, range, parameterName, message);
         }
@@ -98,7 +99,8 @@ public static ImmutableArray<T> MustHaveLengthIn<T>(
         Func<ImmutableArray<T>, Range<int>, Exception> exceptionFactory
     )
     {
-        if (!range.IsValueWithinRange(parameter.Length))
+        var length = parameter.IsDefault ? 0 : parameter.Length;
+        if (!range.IsValueWithinRange(length))
         {
             Throw.CustomException(exceptionFactory, parameter, range);
         }

Code/Light.GuardClauses/Check.MustHaveMaximumLength.cs

@@ -0,0 +1,56 @@
+using System;
+using System.Collections.Immutable;
+using System.Runtime.CompilerServices;
+using Light.GuardClauses.ExceptionFactory;
+using Light.GuardClauses.Exceptions;
+
+namespace Light.GuardClauses;
+
+public static partial class Check
+{
+    /// <summary>
+    /// Ensures that the <see cref="ImmutableArray{T}" /> has at most the specified length, or otherwise throws an <see cref="InvalidCollectionCountException" />.
+    /// </summary>
+    /// <param name="parameter">The <see cref="ImmutableArray{T}" /> to be checked.</param>
+    /// <param name="length">The maximum length the <see cref="ImmutableArray{T}" /> should have.</param>
+    /// <param name="parameterName">The name of the parameter (optional).</param>
+    /// <param name="message">The message that will be passed to the resulting exception (optional).</param>
+    /// <exception cref="InvalidCollectionCountException">Thrown when <paramref name="parameter" /> has more than the specified length.</exception>
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public static ImmutableArray<T> MustHaveMaximumLength<T>(
+        this ImmutableArray<T> parameter,
+        int length,
+        [CallerArgumentExpression("parameter")] string? parameterName = null,
+        string? message = null
+    )
+    {
+        if (parameter.IsDefault && length < 0 || parameter.Length > length)
+        {
+            Throw.InvalidMaximumCollectionCount(parameter, length, parameterName, message);
+        }
+
+        return parameter;
+    }
+
+    /// <summary>
+    /// Ensures that the <see cref="ImmutableArray{T}" /> has at most the specified length, or otherwise throws your custom exception.
+    /// </summary>
+    /// <param name="parameter">The <see cref="ImmutableArray{T}" /> to be checked.</param>
+    /// <param name="length">The maximum length the <see cref="ImmutableArray{T}" /> should have.</param>
+    /// <param name="exceptionFactory">The delegate that creates your custom exception. <paramref name="parameter" /> and <paramref name="length" /> are passed to this delegate.</param>
+    /// <exception cref="Exception">Your custom exception thrown when <paramref name="parameter" /> has more than the specified length.</exception>
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public static ImmutableArray<T> MustHaveMaximumLength<T>(
+        this ImmutableArray<T> parameter,
+        int length,
+        Func<ImmutableArray<T>, int, Exception> exceptionFactory
+    )
+    {
+        if (parameter.IsDefault && length < 0 || parameter.Length > length)
+        {
+            Throw.CustomException(exceptionFactory, parameter, length);
+        }
+
+        return parameter;
+    }
+}

Code/Light.GuardClauses/Check.MustNotContain.cs

@@ -207,6 +207,9 @@ public static string MustNotContain(
     /// <param name="parameterName">The name of the parameter (optional).</param>
     /// <param name="message">The message that will be passed to the resulting exception (optional).</param>
     /// <exception cref="ExistingItemException">Thrown when <paramref name="parameter" /> contains <paramref name="item" />.</exception>
+    /// <remarks>
+    /// The default instance of <see cref="ImmutableArray{T}" /> cannot contain any items, so this method will not throw for default instances.
+    /// </remarks>
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
     public static ImmutableArray<T> MustNotContain<T>(
         this ImmutableArray<T> parameter,
@@ -215,7 +218,7 @@ public static ImmutableArray<T> MustNotContain<T>(
         string? message = null
     )
     {
-        if (parameter.Contains(item))
+        if (!parameter.IsDefault && parameter.Contains(item))
         {
             Throw.ExistingItem(parameter, item, parameterName, message);
         }
@@ -230,6 +233,9 @@ public static ImmutableArray<T> MustNotContain<T>(
     /// <param name="item">The item that must not be part of the <see cref="ImmutableArray{T}" />.</param>
     /// <param name="exceptionFactory">The delegate that creates your custom exception. <paramref name="parameter" /> and <paramref name="item" /> are passed to this delegate.</param>
     /// <exception cref="Exception">Your custom exception thrown when <paramref name="parameter" /> contains <paramref name="item" />.</exception>
+    /// <remarks>
+    /// The default instance of <see cref="ImmutableArray{T}" /> cannot contain any items, so this method will not throw for default instances.
+    /// </remarks>
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
     [ContractAnnotation("exceptionFactory:null => halt")]
     public static ImmutableArray<T> MustNotContain<T>(
@@ -238,7 +244,7 @@ public static ImmutableArray<T> MustNotContain<T>(
         Func<ImmutableArray<T>, T, Exception> exceptionFactory
     )
     {
-        if (parameter.Contains(item))
+        if (!parameter.IsDefault && parameter.Contains(item))
         {
             Throw.CustomException(exceptionFactory, parameter, item);
         }

Code/Light.GuardClauses/ExceptionFactory/Throw.ImmutableArrayLengthNotInRange.cs

@@ -23,6 +23,6 @@ public static void ImmutableArrayLengthNotInRange<T>(
         throw new ArgumentOutOfRangeException(
             parameterName,
             message ??
-            $"{parameterName ?? "The immutable array"} must have its length in between {range.CreateRangeDescriptionText("and")}, but it actually has length {parameter.Length}."
+            $"{parameterName ?? "The immutable array"} must have its length in between {range.CreateRangeDescriptionText("and")}, but it actually {(parameter.IsDefault ? "has no length because it is the default instance" : $"has length {parameter.Length}")}."
         );
 }

Code/Plans/issue-120-must-have-maximum-length-for-immutable-array.md

@@ -0,0 +1,22 @@
+# Issue 120 - MustHaveMaximumLength for ImmutableArray
+
+## Context
+
+The .NET library Light.GuardClauses already has several assertions for collections. They often rely on `IEnumerable<T>` or `IEnumerable`. However, these assertions would result in `ImmutableArray<T>` being boxed - we want to avoid that by providing dedicated assertions for this type which avoids boxing. For this issue, we implement the `MustHaveMaximumLength` assertion for `ImmutableArray<T>`.
+
+## Tasks for this issue
+
+- [ ] The production code should be placed in the Light.GuardClauses project. There is no existing `Check.MustHaveMaximumLength.cs` file, but there is a `Check.MustHaveMaximumCount.cs` file. Create a new file called `Check.MustHaveMaximumLength.cs` in the root folder of the project.
+- [ ] In this file, create several extension method overloads called `MustHaveMaximumLength` for `ImmutableArray<T>`. It should be placed in the class `Check` which is marked as `partial`.
+- [ ] Each assertion in Light.GuardClauses has two overloads - the first one takes the optional `parameterName` and `message` arguments and throw the default exception. The actual exception is thrown in the `Throw` class - use the existing `Throw.InvalidMaximumCollectionCount` method which is located in `ExceptionFactory/Throw.InvalidMaximumCollectionCount.cs`.
+- [ ] The other overload takes a delegate which allows the caller to provide their own custom exceptions. Use the existing `Throw.CustomException` method and pass the delegate, the erroneous `ImmutableArray<T>` instance and the maximum length.
+- [ ] Use the `Length` property of `ImmutableArray<T>` instead of `Count` for performance and correctness.
+- [ ] Create unit tests for both overloads. The corresponding tests should be placed in Light.GuardClauses.Tests project. There is an existing file 'CollectionAssertions/MustHaveMaximumCountTests.cs' but you need to create a new file 'CollectionAssertions/MustHaveMaximumLengthTests.cs' for length-related tests. Please follow conventions of the existing tests (e.g. use FluentAssertions' `Should()` for assertions).
+
+## Notes
+
+- There are already plenty of other assertions and tests in this library. All overloads are placed in the same file in the production code project. The test projects has top-level folders for different groups of assertions, like `CollectionAssertions`, `StringAssertions`, `DateTimeAssertions` and so on. Please take a look at them to follow a similar structure and code style.
+- This assertion specifically targets `ImmutableArray<T>` to avoid boxing that would occur with generic `IEnumerable<T>` extensions.
+- Use the `Length` property instead of `Count` as this is the appropriate property for `ImmutableArray<T>`.
+- The assertion should verify that the `ImmutableArray<T>` does not exceed the specified maximum length.
+- If you have any questions or suggestions, please ask me about them.