dimanche 1 novembre 2015

How to Return Expression

In runtime I have only TClass and a FieldInfo, and I need to generate a lambda expression that gets an instance of TClass and returns the correlate field. After constructing a MemberExpression I got stuck when trying to wrap the expression to Expression<Func<TClass, TClassField>>:

var res = Expression.Lambda<Func<TClass, TClassField>>(memberExpression, paramExp);
return res;

Because TClassField is not known during compile time. I need some strongly typed solution (no casting to object) due to 3rd party requirements. Is this even possible in C#?

EDIT I need something like this -

private void User3rdPartyLibrary<TClass>(FieldInfo fi)
{
    //Goal: call _3rdParty.Method<TClass, TClassField>(expression)

    var memberExp = Expression.Field(Expression.Parameter(typeof(TClass)), fi);
    //var lambda = some magic that returns  Expression.Lambda<Func<TClass, TClassField>>
    //      where fi.FieldType == typeof(TClassField).

    //_3rdParty.Method(lambda);
}

Signature of the 3rd party method:

public void Method<TClass, TClassMember>(Expression<Func<TClass, TClassMember>> expression);





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