ILSpy/ICSharpCode.Decompiler/TypeSystem/ITypeParameter.cs

// Copyright (c) 2010-2013 AlphaSierraPapa for the SharpDevelop Team
// 
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#nullable enable

using System;
using System.Collections.Generic;

using ICSharpCode.Decompiler.Util;

namespace ICSharpCode.Decompiler.TypeSystem
{
	/// <summary>
	/// Type parameter of a generic class/method.
	/// </summary>
	public interface ITypeParameter : IType, ISymbol
	{
		/// <summary>
		/// Get the type of this type parameter's owner.
		/// </summary>
		/// <returns>SymbolKind.TypeDefinition or SymbolKind.Method</returns>
		SymbolKind OwnerType { get; }

		/// <summary>
		/// Gets the owning method/class.
		/// This property may return null (for example for the dummy type parameters used by <see cref="NormalizeTypeVisitor.ReplaceMethodTypeParametersWithDummy"/>).
		/// </summary>
		/// <remarks>
		/// For "class Outer&lt;T&gt; { class Inner {} }",
		/// inner.TypeParameters[0].Owner will be the outer class, because the same
		/// ITypeParameter instance is used both on Outer`1 and Outer`1+Inner.
		/// </remarks>
		IEntity? Owner { get; }

		/// <summary>
		/// Gets the index of the type parameter in the type parameter list of the owning method/class.
		/// </summary>
		int Index { get; }

		/// <summary>
		/// Gets the name of the type parameter.
		/// </summary>
		new string Name { get; }

		/// <summary>
		/// Gets the attributes declared on this type parameter.
		/// </summary>
		IEnumerable<IAttribute> GetAttributes();

		/// <summary>
		/// Gets the variance of this type parameter.
		/// </summary>
		VarianceModifier Variance { get; }

		/// <summary>
		/// Gets the effective base class of this type parameter.
		/// </summary>
		IType EffectiveBaseClass { get; }

		/// <summary>
		/// Gets the effective interface set of this type parameter.
		/// </summary>
		IReadOnlyCollection<IType> EffectiveInterfaceSet { get; }

		/// <summary>
		/// Gets if the type parameter has the 'new()' constraint.
		/// </summary>
		bool HasDefaultConstructorConstraint { get; }

		/// <summary>
		/// Gets if the type parameter has the 'class' constraint.
		/// </summary>
		bool HasReferenceTypeConstraint { get; }

		/// <summary>
		/// Gets if the type parameter has the 'struct' or 'unmanaged' constraint.
		/// </summary>
		bool HasValueTypeConstraint { get; }

		/// <summary>
		/// Gets if the type parameter has the 'unmanaged' constraint.
		/// </summary>
		bool HasUnmanagedConstraint { get; }

		/// <summary>
		/// Nullability of the reference type constraint. (e.g. "where T : class?").
		/// 
		/// Note that the nullability of a use of the type parameter may differ from this.
		/// E.g. "T? GetNull&lt;T&gt;() where T : class => null;"
		/// </summary>
		Nullability NullabilityConstraint { get; }

		IReadOnlyList<TypeConstraint> TypeConstraints { get; }
	}

	public readonly struct TypeConstraint
	{
		public SymbolKind SymbolKind => SymbolKind.Constraint;
		public IType Type { get; }
		public IReadOnlyList<IAttribute> Attributes { get; }

		public TypeConstraint(IType type, IReadOnlyList<IAttribute>? attributes = null)
		{
			this.Type = type ?? throw new ArgumentNullException(nameof(type));
			this.Attributes = attributes ?? EmptyList<IAttribute>.Instance;
		}
	}

	/// <summary>
	/// Represents the variance of a type parameter.
	/// </summary>
	public enum VarianceModifier : byte
	{
		/// <summary>
		/// The type parameter is not variant.
		/// </summary>
		Invariant,
		/// <summary>
		/// The type parameter is covariant (used in output position).
		/// </summary>
		Covariant,
		/// <summary>
		/// The type parameter is contravariant (used in input position).
		/// </summary>
		Contravariant
	};
}