转换 lambda 表达式

发布于 2024-09-13 10:42:14 字数 348 浏览 2 评论 0原文

我有以下代码

Expression<Func<IPersistentAttributeInfo, bool>> expression = info => info.Owner== null;

，并希望将其转换为

Expression<Func<PersistentAttributeInfo, bool>> expression = info => info.Owner== null;

仅在运行时才知道的 PersistentAttributeInfo，但这

可能吗？

原文

I have the following code

Expression<Func<IPersistentAttributeInfo, bool>> expression = info => info.Owner== null;

and want to tranform it to

Expression<Func<PersistentAttributeInfo, bool>> expression = info => info.Owner== null;

PersistentAttributeInfo is only known at runtime though

Is it possible?

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养猫人 2024-09-20 10:42:14

如果 PersistentAttributeInfo 仅在运行时已知，那么您显然无法静态编写 lambda 并让编译器为您完成繁重的工作。您必须从头开始创建一个新的委托：

Type persistentAttributeInfoType = [TypeYouKnowAtRuntime];
ParameterExpression parameter = Expression.Parameter(persistentAttributeInfoType, "info");
LambdaExpression lambda = Expression.Lambda(
    typeof(Func<,>).MakeGenericType(persistentAttributeInfoType, typeof(bool)), 
    Expression.Equal(Expression.Property(parameter, "Owner"), Expression.Constant(null)),
    parameter);

您可以调用 lambda.Compile() 来返回一个委托，该委托类似于示例中转换后的 lambda 表达式（当然，它是无类型的）。

If PersistentAttributeInfo is only known at runtime, you obviously cannot write the lambda statically and have the compiler do the heavy lifting for you. You'll have to create a new one from scratch:

Type persistentAttributeInfoType = [TypeYouKnowAtRuntime];
ParameterExpression parameter = Expression.Parameter(persistentAttributeInfoType, "info");
LambdaExpression lambda = Expression.Lambda(
    typeof(Func<,>).MakeGenericType(persistentAttributeInfoType, typeof(bool)), 
    Expression.Equal(Expression.Property(parameter, "Owner"), Expression.Constant(null)),
    parameter);

You can invoke lambda.Compile() to return a Delegate that is analogous to the transformed lambda expression in your example (though of course untyped).

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