如果委托类型是internal,我在为 F# 中的属性 getter 编译 lambda 表达式时遇到了一些麻烦。这是函数的样子:
// if I omit the 'internal' here everything works as expected
module internal ReflectionHelpers =
open System
open System.Linq.Expressions
open System.Reflection
// it makes no difference if this delegate type is defined outside
// of the module and marked as 'internal'
type GetterFunc<'T> = delegate of 'T -> obj
/// Build a getter expression function for the
/// specified PropertyInfo
let getGetter<'a> (p : PropertyInfo) =
let inst = Expression.Parameter(p.DeclaringType, "i")
let prop = Expression.Property(inst, p)
let conv = Expression.Convert(prop, typeof<obj>)
Expression.Lambda<GetterFunc<'a>>(conv, inst).Compile()
如果我用公共类调用这个方法,我会得到一个像这样的异常(仅当 ReflectionHelpers 模块被定义为“内部”时):
System.ArgumentNullException was unhandled by user code
Message=Value cannot be null.
Parameter name: key
Source=mscorlib
ParamName=key
StackTrace:
at System.Collections.Generic.Dictionary`2.FindEntry(TKey key)
at System.Collections.Generic.Dictionary`2.TryGetValue(TKey key, TValue& value)
at System.Dynamic.Utils.CacheDict`2.TryGetValue(TKey key, TValue& value)
at System.Dynamic.Utils.TypeExtensions.GetParametersCached(MethodBase method)
at System.Linq.Expressions.Expression.ValidateLambdaArgs(Type delegateType, Expression& body, ReadOnlyCollection`1 parameters)
at System.Linq.Expressions.Expression.Lambda[TDelegate](Expression body, String name, Boolean tailCall, IEnumerable`1 parameters)
at System.Linq.Expressions.Expression.Lambda[TDelegate](Expression body, Boolean tailCall, IEnumerable`1 parameters)
at System.Linq.Expressions.Expression.Lambda[TDelegate](Expression body, ParameterExpression[] parameters)
...
可能我在这里遗漏了一个重要点,但目前我看不出发生这种情况的任何原因。