ILSpy/ICSharpCode.Decompiler/TypeSystem/NullableType.cs

// Copyright (c) 2010-2013 AlphaSierraPapa for the SharpDevelop Team
// 
// Permission is hereby granted, free of charge, to any person obtaining a copy of this
// software and associated documentation files (the "Software"), to deal in the Software
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// publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons
// to whom the Software is furnished to do so, subject to the following conditions:
// 
// The above copyright notice and this permission notice shall be included in all copies or
// substantial portions of the Software.
// 
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
// INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
// PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE
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// DEALINGS IN THE SOFTWARE.

using System;

namespace ICSharpCode.Decompiler.TypeSystem
{
	/// <summary>
	/// Static helper methods for working with nullable types.
	/// </summary>
	public static class NullableType
	{
		/// <summary>
		/// Gets whether the specified type is a nullable type.
		/// </summary>
		public static bool IsNullable(IType type)
		{
			if (type == null)
				throw new ArgumentNullException(nameof(type));
			ParameterizedType pt = type.SkipModifiers() as ParameterizedType;
			return pt != null && pt.TypeParameterCount == 1 && pt.GenericType.IsKnownType(KnownTypeCode.NullableOfT);
		}

		public static bool IsNonNullableValueType(IType type)
		{
			return type.IsReferenceType == false && !IsNullable(type);
		}

		/// <summary>
		/// Returns the element type, if <paramref name="type"/> is a nullable type.
		/// Otherwise, returns the type itself.
		/// </summary>
		public static IType GetUnderlyingType(IType type)
		{
			if (type == null)
				throw new ArgumentNullException(nameof(type));
			ParameterizedType pt = type.SkipModifiers() as ParameterizedType;
			if (pt != null && pt.TypeParameterCount == 1 && pt.GenericType.IsKnownType(KnownTypeCode.NullableOfT))
				return pt.GetTypeArgument(0);
			else
				return type;
		}

		/// <summary>
		/// Creates a nullable type.
		/// </summary>
		public static IType Create(ICompilation compilation, IType elementType)
		{
			if (compilation == null)
				throw new ArgumentNullException(nameof(compilation));
			if (elementType == null)
				throw new ArgumentNullException(nameof(elementType));

			IType nullableType = compilation.FindType(KnownTypeCode.NullableOfT);
			ITypeDefinition nullableTypeDef = nullableType.GetDefinition();
			if (nullableTypeDef != null)
				return new ParameterizedType(nullableTypeDef, new[] { elementType });
			else
				return nullableType;
		}

		/// <summary>
		/// Creates a nullable type reference.
		/// </summary>
		public static ParameterizedTypeReference Create(ITypeReference elementType)
		{
			if (elementType == null)
				throw new ArgumentNullException(nameof(elementType));
			return new ParameterizedTypeReference(KnownTypeReference.Get(KnownTypeCode.NullableOfT), new[] { elementType });
		}
	}
}