// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
using System;
namespace Microsoft.Extensions.DependencyInjection
{
/// <summary>
/// Indicates that the parameter should be bound using the keyed service registered with the specified key.
/// </summary>
/// <seealso cref="ServiceKeyAttribute"/>
/// <seealso cref="ServiceKeyLookupMode"/>
[AttributeUsage(AttributeTargets.Parameter)]
public class FromKeyedServicesAttribute : Attribute
{
/// <summary>
/// Creates a new <see cref="FromKeyedServicesAttribute"/> instance.
/// </summary>
/// <param name="key">The key of the keyed service to bind to.</param>
public FromKeyedServicesAttribute(object? key)
{
Key = key;
LookupMode = key == null ? ServiceKeyLookupMode.NullKey : ServiceKeyLookupMode.ExplicitKey;
}
/// <summary>
/// Creates a new <see cref="FromKeyedServicesAttribute"/> instance with <see cref="LookupMode"/> set to <see cref="ServiceKeyLookupMode.InheritKey"/>.
/// </summary>
public FromKeyedServicesAttribute()
{
Key = null;
LookupMode = ServiceKeyLookupMode.InheritKey;
}
/// <summary>
/// The key of the keyed service to bind to.
/// </summary>
/// <remarks>A <see langword="null"/> value with indicates there is not a key and just the parameter type is used to resolve the service.
/// This is useful for DI implementations that require an explict way to declare that the parameter should be resolved for unkeyed services.
/// A <see langword="null"/> value is also used along with <see cref="LookupMode"/> set to <see cref="ServiceKeyLookupMode.InheritKey"/> to indicate that the key should be inherited from the parent scope.
/// </remarks>
public object? Key { get; }
/// <summary>
/// Gets the mode used to look up the service key.
/// </summary>
public ServiceKeyLookupMode LookupMode { get; }
}
}
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