C# Type.IsAssignableFrom方法代码示例

        // the sections mentioned in comments of this method are from C# specification v1.2
		public static Conversion GetImplicit(Operand op, Type to, bool onlyStandard, ITypeMapper typeMapper)
		{
			Type from = Operand.GetType(op, typeMapper);

            Type toUnderlying = Helpers.GetNullableUnderlyingType(to);
		    if (to.Equals(from))
		        return new Direct(typeMapper);

            Type fromUnderlying = Helpers.GetNullableUnderlyingType(@from);
		    if (toUnderlying != null)
		    {
		        if (fromUnderlying != null)
		        {
		            Conversion c = GetImplicit(new FakeTypedOperand(fromUnderlying), toUnderlying, onlyStandard, typeMapper);
		            if (c.IsValid) return new ConvertNullable(typeMapper, c);
		        }
		        else
		        {
                    Conversion c = GetImplicit(op, toUnderlying, onlyStandard, typeMapper);
                    if (c.IsValid) return new WrapNullable(typeMapper, c);
                }
		    }
            
		    // required for arrays created from TypeBuilder-s
			if (from != null && to.IsArray && from.IsArray)
			{
				if (to.GetArrayRank() == from.GetArrayRank())
				{
					if (to.GetElementType().Equals(from.GetElementType()))
						return new Direct(typeMapper);
				}
			}

			TypeCode tcFrom = Type.GetTypeCode(from);
			TypeCode tcTo = Type.GetTypeCode(to);
			byte ct = _convTable[(int)tcFrom][(int)tcTo];

			// section 6.1.2 - Implicit numeric conversions
			if (from != null && (from.IsPrimitive || Helpers.AreTypesEqual(from, typeof(decimal), typeMapper)) && (to.IsPrimitive || Helpers.AreTypesEqual(to, typeof(decimal), typeMapper)))
			{
				if (ct <= I)
				{
				    if (Helpers.AreTypesEqual(from, typeof(decimal), typeMapper) || Helpers.AreTypesEqual(to, typeof(decimal), typeMapper))
						// decimal is handled as user-defined conversion, but as it is a standard one, always enable UDC processing
						onlyStandard = false;
					else
						return new Primitive(typeMapper);
				}
			}

			IntLiteral intLit = op as IntLiteral;

			// section 6.1.3 - Implicit enumeration conversions
			if (!onlyStandard && to.IsEnum && (object)intLit != null && intLit.Value == 0)
				return new Primitive(typeMapper);

			// section 6.1.4 - Implicit reference conversions
			if ((from == null || !from.IsValueType) && !to.IsValueType)
			{
				if (from == null) // from the null type to any reference type
					return new Direct(typeMapper);

				if (to.IsAssignableFrom(from))	// the rest
					return new Direct(typeMapper);
			}

			if (from == null)	// no other conversion from null type is possible
				return new Invalid(typeMapper);

			// section 6.1.5 - Boxing conversions
			if (from.IsValueType)
			{
				if (to.IsAssignableFrom(from))
					return new Boxing(typeMapper);
			}

			// section 6.1.6 - Implicit constant expression conversions
			if ((object)intLit != null && Helpers.AreTypesEqual(from, typeof(int), typeMapper) && to.IsPrimitive)
			{
				int val = intLit.Value;

				switch (tcTo)
				{
					case TypeCode.SByte:
						if (val >= sbyte.MinValue && val <= sbyte.MaxValue)
							return new Direct(typeMapper);
						break;
					case TypeCode.Byte:
						if (val >= byte.MinValue && val <= byte.MaxValue)
                            return new Direct(typeMapper);
                        break;
					case TypeCode.Int16:
						if (val >= short.MinValue && val <= short.MaxValue)
                            return new Direct(typeMapper);
                        break;
					case TypeCode.UInt16:
						if (val >= ushort.MinValue && val <= ushort.MaxValue)
                            return new Direct(typeMapper);
                        break;
//.........这里部分代码省略.........

 public Local GetLocalWithValue(Type type, Compiler.Local fromValue)
 {
     if (fromValue != null)
     {
         if (fromValue.Type == type) return fromValue.AsCopy();
         // otherwise, load onto the stack and let the default handling (below) deal with it
         LoadValue(fromValue);
         if (!type.IsValueType && (fromValue.Type == null || !type.IsAssignableFrom(fromValue.Type)))
         { // need to cast
             Cast(type);
         }
     }
     // need to store the value from the stack
     Local result = new Local(this, type);
     StoreValue(result);
     return result;
 }

        internal static bool IsAssignableFrom(Type target, Type type)
        {
#if WINRT
            return target.GetTypeInfo().IsAssignableFrom(type.GetTypeInfo());
#else
            return target.IsAssignableFrom(type);
#endif
        }