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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.Immutable;
namespace Microsoft.CodeAnalysis.CSharp
{
// Deconstructions are represented internally as a tree of conversions, but
// since they are not conversions from the language perspective we use a wrapper to
// abstract the public API from the implementation.
/// <summary>
/// The representation of a deconstruction as a tree of Deconstruct methods and conversions.
/// Methods only appear in non-terminal nodes. All terminal nodes have a Conversion.
///
/// Here's an example:
/// A deconstruction like <c>(int x1, (long x2, long x3)) = deconstructable1</c> with
/// <c>Deconstructable1.Deconstruct(out int y1, out Deconstructable2 y2)</c> and
/// <c>Deconstructable2.Deconstruct(out int z1, out int z2)</c> is represented as 5 DeconstructionInfo nodes.
///
/// The top-level node has a <see cref="Method"/> (Deconstructable1.Deconstruct), no <see cref="Conversion"/>, but has two <see cref="Nested"/> nodes.
/// Its first nested node has no <see cref="Method"/>, but has a <see cref="Conversion"/> (Identity).
/// Its second nested node has a <see cref="Method"/> (Deconstructable2.Deconstruct), no <see cref="Conversion"/>, and two <see cref="Nested"/> nodes.
/// Those last two nested nodes have no <see cref="Method"/>, but each have a <see cref="Conversion"/> (ImplicitNumeric, from int to long).
/// </summary>
public readonly struct DeconstructionInfo
{
private readonly Conversion _conversion;
/// <summary>
/// The Deconstruct method (if any) for this non-terminal position in the deconstruction tree.
/// </summary>
public IMethodSymbol? Method
{
get
{
return _conversion.Kind == ConversionKind.Deconstruction
? _conversion.MethodSymbol
: null;
}
}
/// <summary>
/// The conversion for a terminal position in the deconstruction tree.
/// </summary>
public Conversion? Conversion
{
get
{
return _conversion.Kind == ConversionKind.Deconstruction
? null
: (Conversion?)_conversion;
}
}
/// <summary>
/// The children for this deconstruction node.
/// </summary>
public ImmutableArray<DeconstructionInfo> Nested
{
get
{
if (_conversion.Kind != ConversionKind.Deconstruction)
{
return ImmutableArray<DeconstructionInfo>.Empty;
}
var deconstructConversionInfo = _conversion.DeconstructConversionInfo;
return deconstructConversionInfo.IsDefault
? ImmutableArray<DeconstructionInfo>.Empty
: deconstructConversionInfo.SelectAsArray(c => new DeconstructionInfo(BoundNode.GetConversion(c.conversion, c.placeholder)));
}
}
internal DeconstructionInfo(Conversion conversion)
{
_conversion = conversion;
}
}
}
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