Much better type safety.

src/ImageSharp/Formats/Bmp/BmpFormat.cs

@@ -8,22 +8,30 @@ namespace SixLabors.ImageSharp.Formats.Bmp
     /// <summary>
     /// Registers the image encoders, decoders and mime type detectors for the bmp format.
     /// </summary>
-    internal sealed class BmpFormat : ImageFormatBase<BmpFormat>
+    internal sealed class BmpFormat : IImageFormat<BmpMetaData>
     {
         private BmpFormat()
         {
         }
 
+        /// <summary>
+        /// Gets the current instance.
+        /// </summary>
+        public static BmpFormat Instance { get; } = new BmpFormat();
+
+        /// <inheritdoc/>
+        public string Name => "BMP";
+
         /// <inheritdoc/>
-        public override string Name => "BMP";
+        public string DefaultMimeType => "image/bmp";
 
         /// <inheritdoc/>
-        public override string DefaultMimeType => "image/bmp";
+        public IEnumerable<string> MimeTypes => BmpConstants.MimeTypes;
 
         /// <inheritdoc/>
-        public override IEnumerable<string> MimeTypes => BmpConstants.MimeTypes;
+        public IEnumerable<string> FileExtensions => BmpConstants.FileExtensions;
 
         /// <inheritdoc/>
-        public override IEnumerable<string> FileExtensions => BmpConstants.FileExtensions;
+        public BmpMetaData CreateDefaultFormatMetaData() => new BmpMetaData();
     }
 }

src/ImageSharp/Formats/Bmp/BmpMetaData.cs

@@ -1,14 +1,12 @@
 // Copyright (c) Six Labors and contributors.
 // Licensed under the Apache License, Version 2.0.
 
-using SixLabors.ImageSharp.MetaData;
-
 namespace SixLabors.ImageSharp.Formats.Bmp
 {
     /// <summary>
     /// Provides Bmp specific metadata information for the image.
     /// </summary>
-    public class BmpMetaData : IImageFormatMetaData
+    public class BmpMetaData
     {
         // TODO: Analyse what properties we would like to preserve.
     }

src/ImageSharp/Formats/Gif/GifEncoderCore.cs

@@ -143,7 +143,7 @@ namespace SixLabors.ImageSharp.Formats.Gif
             for (int i = 0; i < image.Frames.Count; i++)
             {
                 ImageFrame<TPixel> frame = image.Frames[i];
-                GifFrameMetaData frameMetaData = frame.MetaData.GetOrAddFormatMetaData<GifFrameMetaData>(GifFormat.Instance);
+                GifFrameMetaData frameMetaData = frame.MetaData.GetOrAddFormatMetaData(GifFormat.Instance);
                 this.WriteGraphicalControlExtension(frameMetaData, transparencyIndex, stream);
                 this.WriteImageDescriptor(frame, false, stream);
 
@@ -169,7 +169,7 @@ namespace SixLabors.ImageSharp.Formats.Gif
             GifFrameMetaData previousMeta = null;
             foreach (ImageFrame<TPixel> frame in image.Frames)
             {
-                GifFrameMetaData meta = frame.MetaData.GetOrAddFormatMetaData<GifFrameMetaData>(GifFormat.Instance);
+                GifFrameMetaData meta = frame.MetaData.GetOrAddFormatMetaData(GifFormat.Instance);
                 if (quantized is null)
                 {
                     // Allow each frame to be encoded at whatever color depth the frame designates if set.

src/ImageSharp/Formats/Gif/GifFormat.cs

@@ -8,22 +8,33 @@ namespace SixLabors.ImageSharp.Formats.Gif
     /// <summary>
     /// Registers the image encoders, decoders and mime type detectors for the gif format.
     /// </summary>
-    internal sealed class GifFormat : ImageFormatBase<GifFormat>
+    internal sealed class GifFormat : IImageFormat<GifMetaData, GifFrameMetaData>
     {
         private GifFormat()
         {
         }
 
+        /// <summary>
+        /// Gets the current instance.
+        /// </summary>
+        public static GifFormat Instance { get; } = new GifFormat();
+
+        /// <inheritdoc/>
+        public string Name => "GIF";
+
+        /// <inheritdoc/>
+        public string DefaultMimeType => "image/gif";
+
         /// <inheritdoc/>
-        public override string Name => "GIF";
+        public IEnumerable<string> MimeTypes => GifConstants.MimeTypes;
 
         /// <inheritdoc/>
-        public override string DefaultMimeType => "image/gif";
+        public IEnumerable<string> FileExtensions => GifConstants.FileExtensions;
 
         /// <inheritdoc/>
-        public override IEnumerable<string> MimeTypes => GifConstants.MimeTypes;
+        public GifMetaData CreateDefaultFormatMetaData() => new GifMetaData();
 
         /// <inheritdoc/>
-        public override IEnumerable<string> FileExtensions => GifConstants.FileExtensions;
+        public GifFrameMetaData CreateDefaultFormatFrameMetaData() => new GifFrameMetaData();
     }
 }

src/ImageSharp/Formats/Gif/GifFrameMetaData.cs

@@ -1,14 +1,12 @@
 // Copyright (c) Six Labors and contributors.
 // Licensed under the Apache License, Version 2.0.
 
-using SixLabors.ImageSharp.MetaData;
-
 namespace SixLabors.ImageSharp.Formats.Gif
 {
     /// <summary>
     /// Provides Gif specific metadata information for the image frame.
     /// </summary>
-    public class GifFrameMetaData : IImageFormatFrameMetaData
+    public class GifFrameMetaData
     {
         /// <summary>
         /// Gets or sets the length of the color table for paletted images.

src/ImageSharp/Formats/Gif/GifMetaData.cs

@@ -1,14 +1,12 @@
 // Copyright (c) Six Labors and contributors.
 // Licensed under the Apache License, Version 2.0.
 
-using SixLabors.ImageSharp.MetaData;
-
 namespace SixLabors.ImageSharp.Formats.Gif
 {
     /// <summary>
     /// Provides Gif specific metadata information for the image.
     /// </summary>
-    public class GifMetaData : IImageFormatMetaData
+    public class GifMetaData
     {
         /// <summary>
         /// Gets or sets the number of times any animation is repeated.

src/ImageSharp/Formats/IImageFormat.cs

@@ -6,7 +6,37 @@ using System.Collections.Generic;
 namespace SixLabors.ImageSharp.Formats
 {
     /// <summary>
-    /// Describes an image format.
+    /// Defines the contract for an image format containing metadata with multiple frames.
+    /// </summary>
+    /// <typeparam name="TFormatMetaData">The type of format metadata.</typeparam>
+    /// <typeparam name="TFormatFrameMetaData">The type of format frame metadata.</typeparam>
+    public interface IImageFormat<TFormatMetaData, TFormatFrameMetaData> : IImageFormat<TFormatMetaData>
+        where TFormatMetaData : class
+        where TFormatFrameMetaData : class
+    {
+        /// <summary>
+        /// Creates a default instance of the format frame metadata.
+        /// </summary>
+        /// <returns>The <typeparamref name="TFormatFrameMetaData"/>.</returns>
+        TFormatFrameMetaData CreateDefaultFormatFrameMetaData();
+    }
+
+    /// <summary>
+    /// Defines the contract for an image format containing metadata.
+    /// </summary>
+    /// <typeparam name="TFormatMetaData">The type of format metadata.</typeparam>
+    public interface IImageFormat<TFormatMetaData> : IImageFormat
+        where TFormatMetaData : class
+    {
+        /// <summary>
+        /// Creates a default instance of the format metadata.
+        /// </summary>
+        /// <returns>The <typeparamref name="TFormatMetaData"/>.</returns>
+        TFormatMetaData CreateDefaultFormatMetaData();
+    }
+
+    /// <summary>
+    /// Defines the contract for an image format.
     /// </summary>
     public interface IImageFormat
     {

src/ImageSharp/Formats/ImageFormatBase{T}.cs

@@ -1,38 +0,0 @@
-// Copyright (c) Six Labors and contributors.
-// Licensed under the Apache License, Version 2.0.
-
-using System;
-using System.Collections.Generic;
-
-namespace SixLabors.ImageSharp.Formats
-{
-    /// <summary>
-    /// The base class for all image formats.
-    /// Inheriting classes should implement the singleton pattern by creating a private constructor.
-    /// </summary>
-    /// <typeparam name="T">The type of image format.</typeparam>
-    public abstract class ImageFormatBase<T> : IImageFormat
-        where T : class, IImageFormat
-    {
-        private static readonly Lazy<T> Lazy = new Lazy<T>(CreateInstance);
-
-        /// <summary>
-        /// Gets the current instance.
-        /// </summary>
-        public static T Instance => Lazy.Value;
-
-        /// <inheritdoc/>
-        public abstract string Name { get; }
-
-        /// <inheritdoc/>
-        public abstract string DefaultMimeType { get; }
-
-        /// <inheritdoc/>
-        public abstract IEnumerable<string> MimeTypes { get; }
-
-        /// <inheritdoc/>
-        public abstract IEnumerable<string> FileExtensions { get; }
-
-        private static T CreateInstance() => (T)Activator.CreateInstance(typeof(T), true);
-    }
-}

src/ImageSharp/Formats/Jpeg/JpegFormat.cs

@@ -8,22 +8,30 @@ namespace SixLabors.ImageSharp.Formats.Jpeg
     /// <summary>
     /// Registers the image encoders, decoders and mime type detectors for the jpeg format.
     /// </summary>
-    internal sealed class JpegFormat : ImageFormatBase<JpegFormat>
+    internal sealed class JpegFormat : IImageFormat<JpegMetaData>
     {
         private JpegFormat()
         {
         }
 
+        /// <summary>
+        /// Gets the current instance.
+        /// </summary>
+        public static JpegFormat Instance { get; } = new JpegFormat();
+
+        /// <inheritdoc/>
+        public string Name => "JPEG";
+
         /// <inheritdoc/>
-        public override string Name => "JPEG";
+        public string DefaultMimeType => "image/jpeg";
 
         /// <inheritdoc/>
-        public override string DefaultMimeType => "image/jpeg";
+        public IEnumerable<string> MimeTypes => JpegConstants.MimeTypes;
 
         /// <inheritdoc/>
-        public override IEnumerable<string> MimeTypes => JpegConstants.MimeTypes;
+        public IEnumerable<string> FileExtensions => JpegConstants.FileExtensions;
 
         /// <inheritdoc/>
-        public override IEnumerable<string> FileExtensions => JpegConstants.FileExtensions;
+        public JpegMetaData CreateDefaultFormatMetaData() => new JpegMetaData();
     }
 }

src/ImageSharp/Formats/Jpeg/JpegMetaData.cs

@@ -1,14 +1,12 @@
 // Copyright (c) Six Labors and contributors.
 // Licensed under the Apache License, Version 2.0.
 
-using SixLabors.ImageSharp.MetaData;
-
 namespace SixLabors.ImageSharp.Formats.Jpeg
 {
     /// <summary>
     /// Provides Jpeg specific metadata information for the image.
     /// </summary>
-    public class JpegMetaData : IImageFormatMetaData
+    public class JpegMetaData
     {
         // TODO: Analyse what properties we would like to preserve.
     }

src/ImageSharp/Formats/Png/PngFormat.cs

@@ -8,22 +8,30 @@ namespace SixLabors.ImageSharp.Formats.Png
     /// <summary>
     /// Registers the image encoders, decoders and mime type detectors for the png format.
     /// </summary>
-    internal sealed class PngFormat : ImageFormatBase<PngFormat>
+    internal sealed class PngFormat : IImageFormat<PngMetaData>
     {
         private PngFormat()
         {
         }
 
+        /// <summary>
+        /// Gets the current instance.
+        /// </summary>
+        public static PngFormat Instance { get; } = new PngFormat();
+
+        /// <inheritdoc/>
+        public string Name => "PNG";
+
         /// <inheritdoc/>
-        public override string Name => "PNG";
+        public string DefaultMimeType => "image/png";
 
         /// <inheritdoc/>
-        public override string DefaultMimeType => "image/png";
+        public IEnumerable<string> MimeTypes => PngConstants.MimeTypes;
 
         /// <inheritdoc/>
-        public override IEnumerable<string> MimeTypes => PngConstants.MimeTypes;
+        public IEnumerable<string> FileExtensions => PngConstants.FileExtensions;
 
         /// <inheritdoc/>
-        public override IEnumerable<string> FileExtensions => PngConstants.FileExtensions;
+        public PngMetaData CreateDefaultFormatMetaData() => new PngMetaData();
     }
 }

src/ImageSharp/Formats/Png/PngMetaData.cs

@@ -1,14 +1,12 @@
 // Copyright (c) Six Labors and contributors.
 // Licensed under the Apache License, Version 2.0.
 
-using SixLabors.ImageSharp.MetaData;
-
 namespace SixLabors.ImageSharp.Formats.Png
 {
     /// <summary>
     /// Provides Png specific metadata information for the image.
     /// </summary>
-    public class PngMetaData : IImageFormatMetaData
+    public class PngMetaData
     {
         // TODO: Analyse what properties we would like to preserve.
     }

src/ImageSharp/MetaData/IImageFormatFrameMetaData.cs

@@ -1,13 +0,0 @@
-// Copyright (c) Six Labors and contributors.
-// Licensed under the Apache License, Version 2.0.
-
-namespace SixLabors.ImageSharp.MetaData
-{
-    /// <summary>
-    /// Encapsulates the format specific metadata of an image frame.
-    /// This interface exists to allow type saftey and avoid the performance overhead of parsing attributes.
-    /// </summary>
-    public interface IImageFormatFrameMetaData
-    {
-    }
-}

src/ImageSharp/MetaData/IImageFormatMetaData.cs

@@ -1,13 +0,0 @@
-// Copyright (c) Six Labors and contributors.
-// Licensed under the Apache License, Version 2.0.
-
-namespace SixLabors.ImageSharp.MetaData
-{
-    /// <summary>
-    /// Encapsulates the format specific metadata of an image.
-    /// This interface exists to allow type saftey and avoid the performance overhead of parsing attributes.
-    /// </summary>
-    public interface IImageFormatMetaData
-    {
-    }
-}

src/ImageSharp/MetaData/ImageFrameMetaData.cs

@@ -12,7 +12,7 @@ namespace SixLabors.ImageSharp.MetaData
     /// </summary>
     public sealed class ImageFrameMetaData
     {
-        private readonly Dictionary<IImageFormat, IImageFormatFrameMetaData> metaData = new Dictionary<IImageFormat, IImageFormatFrameMetaData>();
+        private readonly Dictionary<IImageFormat, object> metaData = new Dictionary<IImageFormat, object>();
 
         /// <summary>
         /// Initializes a new instance of the <see cref="ImageFrameMetaData"/> class.
@@ -32,7 +32,7 @@ namespace SixLabors.ImageSharp.MetaData
         {
             DebugGuard.NotNull(other, nameof(other));
 
-            foreach (KeyValuePair<IImageFormat, IImageFormatFrameMetaData> meta in other.metaData)
+            foreach (KeyValuePair<IImageFormat, object> meta in other.metaData)
             {
                 this.metaData.Add(meta.Key, meta.Value);
             }
@@ -47,12 +47,16 @@ namespace SixLabors.ImageSharp.MetaData
         /// <summary>
         /// Adds or updates the specified key and value to the <see cref="ImageMetaData"/>.
         /// </summary>
+        /// <typeparam name="TFormatMetaData">The type of format metadata.</typeparam>
+        /// <typeparam name="TFormatFrameMetaData">The type of format frame metadata.</typeparam>
         /// <param name="key">The key of the metadata to add.</param>
         /// <param name="value">The value of the element to add.</param>
         /// <exception cref="ArgumentNullException">key is null.</exception>
         /// <exception cref="ArgumentNullException">value is null.</exception>
         /// <exception cref="ArgumentException">An element with the same key already exists in the <see cref="ImageMetaData"/>.</exception>
-        public void AddOrUpdateFormatMetaData(IImageFormat key, IImageFormatFrameMetaData value)
+        public void AddOrUpdateFormatMetaData<TFormatMetaData, TFormatFrameMetaData>(IImageFormat<TFormatMetaData, TFormatFrameMetaData> key, TFormatFrameMetaData value)
+            where TFormatMetaData : class
+            where TFormatFrameMetaData : class
         {
             // Don't think this needs to be threadsafe.
             Guard.NotNull(value, nameof(value));
@@ -62,20 +66,22 @@ namespace SixLabors.ImageSharp.MetaData
         /// <summary>
         /// Gets the metadata value associated with the specified key.
         /// </summary>
-        /// <typeparam name="T">The type of metadata.</typeparam>
+        /// <typeparam name="TFormatMetaData">The type of format metadata.</typeparam>
+        /// <typeparam name="TFormatFrameMetaData">The type of format frame metadata.</typeparam>
         /// <param name="key">The key of the value to get.</param>
         /// <returns>
-        /// The <typeparamref name="T"/>.
+        /// The <typeparamref name="TFormatFrameMetaData"/>.
         /// </returns>
-        public T GetOrAddFormatMetaData<T>(IImageFormat key)
-            where T : IImageFormatFrameMetaData, new()
+        public TFormatFrameMetaData GetOrAddFormatMetaData<TFormatMetaData, TFormatFrameMetaData>(IImageFormat<TFormatMetaData, TFormatFrameMetaData> key)
+            where TFormatMetaData : class
+            where TFormatFrameMetaData : class
         {
-            if (this.metaData.TryGetValue(key, out IImageFormatFrameMetaData meta))
+            if (this.metaData.TryGetValue(key, out object meta))
             {
-                return (T)meta;
+                return (TFormatFrameMetaData)meta;
             }
 
-            var newMeta = new T();
+            TFormatFrameMetaData newMeta = key.CreateDefaultFormatFrameMetaData();
             this.AddOrUpdateFormatMetaData(key, newMeta);
             return newMeta;
         }

src/ImageSharp/MetaData/ImageMetaData.cs

@@ -26,7 +26,7 @@ namespace SixLabors.ImageSharp.MetaData
         /// </summary>
         public const double DefaultVerticalResolution = 96;
 
-        private readonly Dictionary<IImageFormat, IImageFormatMetaData> metaData = new Dictionary<IImageFormat, IImageFormatMetaData>();
+        private readonly Dictionary<IImageFormat, object> metaData = new Dictionary<IImageFormat, object>();
         private double horizontalResolution;
         private double verticalResolution;
 
@@ -52,7 +52,7 @@ namespace SixLabors.ImageSharp.MetaData
             this.VerticalResolution = other.VerticalResolution;
             this.ResolutionUnits = other.ResolutionUnits;
 
-            foreach (KeyValuePair<IImageFormat, IImageFormatMetaData> meta in other.metaData)
+            foreach (KeyValuePair<IImageFormat, object> meta in other.metaData)
             {
                 this.metaData.Add(meta.Key, meta.Value);
             }
@@ -134,12 +134,14 @@ namespace SixLabors.ImageSharp.MetaData
         /// <summary>
         /// Adds or updates the specified key and value to the <see cref="ImageMetaData"/>.
         /// </summary>
+        /// <typeparam name="TFormatMetaData">The type of format metadata.</typeparam>
         /// <param name="key">The key of the metadata to add.</param>
         /// <param name="value">The value of the element to add.</param>
         /// <exception cref="ArgumentNullException">key is null.</exception>
         /// <exception cref="ArgumentNullException">value is null.</exception>
         /// <exception cref="ArgumentException">An element with the same key already exists in the <see cref="ImageMetaData"/>.</exception>
-        public void AddOrUpdateFormatMetaData(IImageFormat key, IImageFormatMetaData value)
+        public void AddOrUpdateFormatMetaData<TFormatMetaData>(IImageFormat<TFormatMetaData> key, TFormatMetaData value)
+            where TFormatMetaData : class
         {
             // Don't think this needs to be threadsafe.
             Guard.NotNull(value, nameof(value));
@@ -149,20 +151,20 @@ namespace SixLabors.ImageSharp.MetaData
         /// <summary>
         /// Gets the metadata value associated with the specified key.
         /// </summary>
-        /// <typeparam name="T">The type of metadata.</typeparam>
+        /// <typeparam name="TFormatMetaData">The type of metadata.</typeparam>
         /// <param name="key">The key of the value to get.</param>
         /// <returns>
-        /// The <typeparamref name="T"/>.
+        /// The <typeparamref name="TFormatMetaData"/>.
         /// </returns>
-        public T GetOrAddFormatMetaData<T>(IImageFormat key)
-            where T : IImageFormatMetaData, new()
+        public TFormatMetaData GetOrAddFormatMetaData<TFormatMetaData>(IImageFormat<TFormatMetaData> key)
+             where TFormatMetaData : class
         {
-            if (this.metaData.TryGetValue(key, out IImageFormatMetaData meta))
+            if (this.metaData.TryGetValue(key, out object meta))
             {
-                return (T)meta;
+                return (TFormatMetaData)meta;
             }
 
-            var newMeta = new T();
+            TFormatMetaData newMeta = key.CreateDefaultFormatMetaData();
             this.AddOrUpdateFormatMetaData(key, newMeta);
             return newMeta;
         }

tests/ImageSharp.Tests/Formats/Gif/GifEncoderTests.cs

@@ -189,8 +189,8 @@ namespace SixLabors.ImageSharp.Tests.Formats.Gif
                 inStream.Position = 0;
 
                 var image = Image.Load(inStream);
-                GifMetaData metaData = image.MetaData.GetOrAddFormatMetaData<GifMetaData>(GifFormat.Instance);
-                GifFrameMetaData frameMetaData = image.Frames.RootFrame.MetaData.GetOrAddFormatMetaData<GifFrameMetaData>(GifFormat.Instance);
+                GifMetaData metaData = image.MetaData.GetOrAddFormatMetaData(GifFormat.Instance);
+                GifFrameMetaData frameMetaData = image.Frames.RootFrame.MetaData.GetOrAddFormatMetaData(GifFormat.Instance);
                 GifColorTableMode colorMode = metaData.ColorTableMode;
                 var encoder = new GifEncoder()
                 {
@@ -212,8 +212,8 @@ namespace SixLabors.ImageSharp.Tests.Formats.Gif
 
                 for (int i = 0; i < image.Frames.Count; i++)
                 {
-                    GifFrameMetaData ifm = image.Frames[i].MetaData.GetOrAddFormatMetaData<GifFrameMetaData>(GifFormat.Instance);
-                    GifFrameMetaData cifm = clone.Frames[i].MetaData.GetOrAddFormatMetaData<GifFrameMetaData>(GifFormat.Instance);
+                    GifFrameMetaData ifm = image.Frames[i].MetaData.GetOrAddFormatMetaData(GifFormat.Instance);
+                    GifFrameMetaData cifm = clone.Frames[i].MetaData.GetOrAddFormatMetaData(GifFormat.Instance);
 
                     Assert.Equal(ifm.ColorTableLength, cifm.ColorTableLength);
                     Assert.Equal(ifm.FrameDelay, cifm.FrameDelay);

tests/ImageSharp.Tests/MetaData/ImageFrameMetaDataTests.cs

@@ -30,7 +30,7 @@ namespace SixLabors.ImageSharp.Tests
             metaData.AddOrUpdateFormatMetaData(GifFormat.Instance, gifFrameMetaData);
 
             var clone = new ImageFrameMetaData(metaData);
-            GifFrameMetaData cloneGifFrameMetaData = clone.GetOrAddFormatMetaData<GifFrameMetaData>(GifFormat.Instance);
+            GifFrameMetaData cloneGifFrameMetaData = clone.GetOrAddFormatMetaData(GifFormat.Instance);
 
             Assert.Equal(frameDelay, cloneGifFrameMetaData.FrameDelay);
             Assert.Equal(colorTableLength, cloneGifFrameMetaData.ColorTableLength);