Made the ErrorMetric mandatory and immutable in the CompareSettings.

Author: dlemstra

src/Magick.NET.Core/Factories/ISettingsFactory.cs

@@ -15,8 +15,9 @@ public interface ISettingsFactory<TQuantumType>
     /// <summary>
     /// Initializes a new instance that implements <see cref="ICompareSettings{TQuantumType}"/>.
     /// </summary>
+    /// <param name="metric">The error metric to use.</param>
     /// <returns>A new <see cref="ICompareSettings{TQuantumType}"/> instance.</returns>
-    ICompareSettings<TQuantumType> CreateCompareSettings();
+    ICompareSettings<TQuantumType> CreateCompareSettings(ErrorMetric metric);
 
     /// <summary>
     /// Initializes a new instance that implements <see cref="IComplexSettings"/>.

src/Magick.NET.Core/Settings/ICompareSettings{TQuantumType}.cs

@@ -13,9 +13,9 @@ public interface ICompareSettings<TQuantumType>
     where TQuantumType : struct, IConvertible
 {
     /// <summary>
-    /// Gets or sets the error metric to use.
+    /// Gets the error metric to use.
     /// </summary>
-    ErrorMetric Metric { get; set; }
+    ErrorMetric Metric { get; }
 
     /// <summary>
     /// Gets or sets the color that emphasize pixel differences.

src/Magick.NET/Factories/SettingsFactory.cs

@@ -21,9 +21,10 @@ public sealed class SettingsFactory : ISettingsFactory<QuantumType>
     /// <summary>
     /// Initializes a new instance that implements <see cref="ICompareSettings{TQuantumType}"/>.
     /// </summary>
+    /// <param name="metric">The error metric to use.</param>
     /// <returns>A new <see cref="ICompareSettings{TQuantumType}"/> instance.</returns>
-    public ICompareSettings<QuantumType> CreateCompareSettings()
-        => new CompareSettings();
+    public ICompareSettings<QuantumType> CreateCompareSettings(ErrorMetric metric)
+        => new CompareSettings(metric);
 
     /// <summary>
     /// Initializes a new instance that implements <see cref="IComplexSettings"/>.

src/Magick.NET/MagickImage.cs

@@ -1746,7 +1746,7 @@ public IMagickImage<QuantumType> Compare(IMagickImage image, ErrorMetric metric,
     /// <returns>The image that contains the difference.</returns>
     /// <exception cref="MagickException">Thrown when an error is raised by ImageMagick.</exception>
     public IMagickImage<QuantumType> Compare(IMagickImage image, ErrorMetric metric, Channels channels, out double distortion)
-        => Compare(image, new CompareSettings { Metric = metric }, channels, out distortion);
+        => Compare(image, new CompareSettings(metric), channels, out distortion);
 
     /// <summary>
     /// Returns the distortion based on the specified metric.

src/Magick.NET/Settings/CompareSettings.cs

@@ -19,9 +19,16 @@ namespace ImageMagick;
 public sealed class CompareSettings : ICompareSettings<QuantumType>
 {
     /// <summary>
-    /// Gets or sets the error metric to use.
+    /// Initializes a new instance of the <see cref="CompareSettings"/> class.
     /// </summary>
-    public ErrorMetric Metric { get; set; }
+    /// <param name="metric">The error metric to use.</param>
+    public CompareSettings(ErrorMetric metric)
+        => Metric = metric;
+
+    /// <summary>
+    /// Gets the error metric to use.
+    /// </summary>
+    public ErrorMetric Metric { get; }
 
     /// <summary>
     /// Gets or sets the color that emphasize pixel differences.

tests/Magick.NET.Tests/Factories/SettingsFactoryTests/TheCreateCompareSettingsMethod.cs

@@ -16,10 +16,11 @@ public void ShouldCreateInstance()
         {
             var factory = new SettingsFactory();
 
-            var settings = factory.CreateCompareSettings();
+            var settings = factory.CreateCompareSettings(ErrorMetric.NormalizedCrossCorrelation);
 
             Assert.NotNull(settings);
             Assert.IsType<CompareSettings>(settings);
+            Assert.Equal(ErrorMetric.NormalizedCrossCorrelation, settings.Metric);
         }
     }
 }

tests/Magick.NET.Tests/MagickImageTests/TheCompareMethod.cs

@@ -44,7 +44,7 @@ public void ShouldThrowAnExceptionWhenImageIsNullAndSettingsAreNotNull()
         {
             using var image = new MagickImage();
 
-            Assert.Throws<ArgumentNullException>("image", () => image.Compare(null, new CompareSettings(), out var distortion));
+            Assert.Throws<ArgumentNullException>("image", () => image.Compare(null, new CompareSettings(ErrorMetric.PeakSignalToNoiseRatio), out var distortion));
         }
 
         [Fact]
@@ -71,10 +71,7 @@ public void ShouldReturnEmptyErrorInfoWhenTheImagesAreEqual()
         [Fact]
         public void ShouldReturnZeroWhenTheImagesAreEqual()
         {
-            var settings = new CompareSettings
-            {
-                Metric = ErrorMetric.RootMeanSquared,
-            };
+            var settings = new CompareSettings(ErrorMetric.RootMeanSquared);
 
             using var image = new MagickImage(Files.Builtin.Logo);
             using var other = new MagickImage(Files.Builtin.Logo);
@@ -114,9 +111,8 @@ public void ShouldReturnErrorInfoWhenTheImagesAreNotEqual()
         [Fact]
         public void ShouldReturnNonZeroValueWhenTheImagesAreNotEqual()
         {
-            var settings = new CompareSettings
+            var settings = new CompareSettings(ErrorMetric.RootMeanSquared)
             {
-                Metric = ErrorMetric.RootMeanSquared,
                 HighlightColor = MagickColors.Yellow,
                 LowlightColor = MagickColors.Red,
                 MasklightColor = MagickColors.Magenta,