.net lambda 表达式转换
也许我想要实现的目标是无意义的，但我认为它应该有效。 我有一个表达式，
Expression<Func<Model.Document, bool>> expr1 = d => //something
我需要将此表达式转换为
Expression<Func<Model.Invoice, bool>
Model.Invoice 继承自 Model.Document 的位置，
这可能吗？
maybe what I'm trying to achieve is a non-sense, but I think it should work.
I have an expression
Expression<Func<Model.Document, bool>> expr1 = d => //something
I nedd to cast this Expression in a
Expression<Func<Model.Invoice, bool>
where Model.Invoice inherits from Model.Document
Is that possible?
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这实际上与 lambda 表达式无关 - 它与表达式树尤其是
Expression有关。Expression在 T 中是不变的 - 即使不是，Func和Func不适合协方差，除非我弄错了（这很有可能）。我怀疑您需要分解
Expression并重新创建它，这可能不是很简单......或者您可以在周围添加一个包装层现有的Expression，这半等价于：This isn't really to do with lambda expressions - it's to do with expression trees and
Expression<TDelegate>in particular.Expression<TDelegate>is invariant in T - and even if it weren't, the relationship betweenFunc<Model.Document, bool>andFunc<Model.Invoice, bool>wouldn't be appropriate for covariance, unless I'm mistaken (which is quite possible).I suspect you'll need to break up the
Expression<T>and recreate it, which may not be terribly simple... alternatively you could add a wrapper layer around the existingExpression<T>, which would be semi-equivalent to saying: