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// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.
using System.Collections.Generic;
namespace System.Runtime.CompilerServices
{
/// <summary>
/// Indicates that the use of <see cref="System.ValueTuple"/> on a member is meant to be treated as a tuple with element names.
/// </summary>
[CLSCompliant(false)]
[AttributeUsage(AttributeTargets.Field | AttributeTargets.Parameter | AttributeTargets.Property | AttributeTargets.ReturnValue | AttributeTargets.Class | AttributeTargets.Struct | AttributeTargets.Event)]
public sealed class TupleElementNamesAttribute : Attribute
{
private readonly string[] _transformNames;
/// <summary>
/// Initializes a new instance of the <see
/// cref="TupleElementNamesAttribute"/> class.
/// </summary>
/// <param name="transformNames">
/// Specifies, in a pre-order depth-first traversal of a type's
/// construction, which <see cref="System.ValueType"/> occurrences are
/// meant to carry element names.
/// </param>
/// <remarks>
/// This constructor is meant to be used on types that contain an
/// instantiation of <see cref="System.ValueType"/> that contains
/// element names. For instance, if <c>C</c> is a generic type with
/// two type parameters, then a use of the constructed type <c>C{<see
/// cref="System.ValueTuple{T1, T2}"/>, <see
/// cref="System.ValueTuple{T1, T2, T3}"/></c> might be intended to
/// treat the first type argument as a tuple with element names and the
/// second as a tuple without element names. In which case, the
/// appropriate attribute specification should use a
/// <c>transformNames</c> value of <c>{ "name1", "name2", null, null,
/// null }</c>.
/// </remarks>
public TupleElementNamesAttribute(string[] transformNames)
{
if (transformNames == null)
{
throw new ArgumentNullException(nameof(transformNames));
}
_transformNames = transformNames;
}
/// <summary>
/// Specifies, in a pre-order depth-first traversal of a type's
/// construction, which <see cref="System.ValueTuple"/> elements are
/// meant to carry element names.
/// </summary>
public IList<string> TransformNames => _transformNames;
}
}
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