LINQ和平等运营商:防爆$ P $类型'System.Int32的“的pssion不能用于类型参数'System.Object的' [英] Linq and the Equality Operator: Expression of type 'System.Int32' cannot be used for parameter of type 'System.Object'
问题描述
我试图重写等式(==)运算符在C#中处理比较任何类型的自定义类型(自定义类型真的是围绕空包装/箱)。
I'm trying to override the equality (==) operator in C# to handle comparing any type to a custom type (the custom type is really a wrapper/box around null).
所以我有这样的:
internal sealed class Nothing
{
public override bool Equals(object obj)
{
if (obj == null || obj is Nothing)
return true;
else
return false;
}
public static bool operator ==(object x, Nothing y)
{
if ((x == null || x is Nothing) && (y == null || y is Nothing))
return true;
return false;
}
...
}
现在,如果我做出这样一个电话:
Now if I make a call like:
Nothing n = new Nothing();
bool equal = (10 == n);
这工作完全正常。但是,如果我试图通过一个LINQ EX pression树做同样的事情:
It works perfectly fine. However, if I try to do this same thing through a Linq expression tree:
exp = Expression.Equal(
Expression.Constant(10),
Expression.Constant(new Nothing(), typeof(Nothing))
);
这引发异常:
It throws the exception:
System.ArgumentException : Expression of type 'System.Int32' cannot be used for parameter of type 'System.Object' of method 'Boolean op_Equality(System.Object, PARTSFinder.Rules.Runtime.RulesNothing)'
at System.Linq.Expressions.Expression.ValidateArgumentTypes(MethodInfo method, ReadOnlyCollection`1& arguments)
at System.Linq.Expressions.Expression.ValidateCallArgs(Expression instance, MethodInfo method, ReadOnlyCollection`1& arguments)
at System.Linq.Expressions.Expression.Call(Expression instance, MethodInfo method, IEnumerable`1 arguments)
at System.Linq.Expressions.Expression.Call(Expression instance, MethodInfo method, Expression[] arguments)
at System.Linq.Expressions.ExpressionCompiler.GenerateBinaryMethod(ILGenerator gen, BinaryExpression b, StackType ask)
为什么基本系统可以转换的Int32为对象,但LINQ的不行,或者我如何才能解决这个问题的任何想法?
Any ideas on why the base system can convert Int32 to Object, but Linq can't, or how I can fix this?
这件事瞪大了眼睛,因为LINQ的也无法比较的Int32摆在首位,以对象:
This whole thing stared because Linq also can't compare Int32 to Object in the first place:
exp = Expression.Equal(
Expression.Constant(10),
Expression.Constant(null)
);
抛出一个异常,说明没有比较运营商System.Int32的和System.Object的。
Throws an exception stating that there is no comparison operator for "System.Int32" and "System.Object".
快速后续:
没有问题,下面做的工作:
The following do work without issue:
exp = Expression.Equal(
Expression.Constant(10, typeof(object)),
Expression.Constant(new Nothing(), typeof(Nothing))
);
exp = Expression.Equal(
Expression.Constant(10, typeof(object)),
Expression.Constant(null)
);
所以专门铸造的一切对象。因此,没有LINQ的只是内部没有处理继承?那是pretty的讨厌...
So specifically casting everything to object. So does Linq just not handle inheritance internally? Thats pretty annoying...
跟帖#2:
我也尝试过使用一个自定义的比较方法:
I also tried using a custom comparison method:
exp = Expression.Equal(
Expression.Constant(10),
Expression.Constant(null),
false,
this.GetType().GetMethod("ValueEquals", BindingFlags.Public | BindingFlags.Static)
);
public static bool ValueEquals(object x, object y)
{
if (x == null && y == null)
return true;
if (x.GetType() != y.GetType())
return false;
return x == y;
}
这也将引发异常:
System.InvalidOperationException : The operands for operator 'Equal' do not match the parameters of method 'ValueEquals'.
at System.Linq.Expressions.Expression.GetMethodBasedBinaryOperator(ExpressionType binaryType, Expression left, Expression right, MethodInfo method, Boolean liftToNull)
不过,再铸一切直接反对作品:
But again casting everything directly to object works:
exp = Expression.Equal(
Expression.Constant(10, typeof(object)),
Expression.Constant(null, typeof(object)),
false,
this.GetType().GetMethod("ValueEquals", BindingFlags.Public | BindingFlags.Static)
);
所以我想我有我的解决办法......一切都投对象,并使用自定义的比较方法。我仍然惊讶的LINQ自动为普通的C#确实没有做转换。
So I guess I have my workaround... cast everything to object and use a custom comparison method. I'm still surprised Linq doesn't do the conversion automatically as normal C# does.
推荐答案
什么是错的空?再缺少 INT
VS 空
,试试 INT
?:
What is wrong with null? Re the missing int
vs null
, try int?
:
exp = Expression.Equal(
Expression.Constant(10, typeof(int?)),
Expression.Constant(null, typeof(int?))
);
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