class Program
{
    // Initialization code. Don't use any Avalonia, third-party APIs or any
    // SynchronizationContext-reliant code before AppMain is called: things aren't initialized
    // yet and stuff might break.
    public static void Main(string[] args)
    {
        BuildAvaloniaApp()
            .StartWithClassicDesktopLifetime(args);
    }

    // Avalonia configuration, don't remove; also used by visual designer.
    public static AppBuilder BuildAvaloniaApp()
    {
        return AppBuilder.Configure<App>()
            .UsePlatformDetect()
            .LogToTrace()
            .WithIcons(container => container
                .Register<FontAwesomeIconProvider>()
                .Register<MaterialDesignIconProvider>());
    }
}

namespace Projektanker.Icons.Avalonia
{
    /// <summary>
    /// Represents an icon reader.
    /// </summary>
    public interface IIconReader
    {
        /// <summary>
        /// Gets the SVG path of the requested icon.
        /// </summary>
        /// <param name="value">The value specifying the icon to return it's path from.</param>
        /// <returns>The path of the icon.</returns>
        /// <exception cref="System.Collections.Generic.KeyNotFoundException">
        /// The icon associated with the specified <paramref name="value"/> does not exists.
        /// </exception>
        string GetIconPath(string value);
    }

    /// <summary>
    /// Represents an icon provider.
    /// </summary>
    public interface IIconProvider : IIconReader
    {
        /// <summary>
        /// Gets the prefix of the <see cref="IIconProvider"/>.
        /// </summary>
        string Prefix { get; }
    }
}

container.Register<MyCustomIconProvider>()

IIconProvider provider = new MyCustomIconProvider(/* custom ctor arguments */);
container.Register(provider);