Foreach loop using expression trees

Question

I saw this problem when creating a dynamic expression tree and expression / expression trees , and since I'm new to expression trees, I'm still trying to figure out how to achieve what I want.

The contrived object below

    public class TestObject
    {
        public TestObject()
        {
            ClassList = new List<Class>();
        }
        public int Age { get; set; }
        public List<Class> ClassList { get; set; } 
    }

    public class Class
    {
        public string Name { get; set; }
        public int ClassId { get; set; }
    }

At runtime, I repeat each of the properties and generate a delegate that performs the conversion to the string of this property. Everything works. The problem that I have to deal with right now is that for the List type, I need to be able to apply a set of actions to each element in the ClassList property, so I need a foreach that allows me to do this.

I currently have this

//type==TestObject at runtime
//propertyName == "ClassList"
   ParameterExpression recordExpression = Expression.Parameter(type, "record");

   memberExpression = MemberExpression.Property(recordExpression, propertyName);

   Type getEnumerableDelegateType =
                typeof(Func<,>).MakeGenericType(new Type[] { type, memberExpression.Type}); 

   var getList = Expression.Lambda(getEnumerableDelegateType, memberExpression, recordExpression);

GetList , . , , - , , , .

, - totalAction

   var getListFunc = new Func<TestObject, List<Class>>((TestObject obj1) => obj1.ClassList);

   Action<List<Class>> listAction = delegate(List<Class> data)
                {
                    foreach (var dataChannelWithUnitse in data)
                    {
                        //Apply generated delegate
                    }
                };

     Action<TestObject> overallAction = delegate(TestObject data)
                {
                    var x = getListFunc.Invoke(data);
                    listAction.Invoke(x as List<Class>);
                };

, , .

, "Enter" "TestObject", "',

    var typeParam = Expression.Parameter(type, "Input");
    var listVariable = Expression.Variable(memberExpression.Type, "List");
    var enumerator = Expression.Variable(typeof(IEnumerator<>).MakeGenericType(dataType));


    var enumeratorType = typeof(IEnumerator<>).MakeGenericType(dataType);
    var enumerableType = typeof(IEnumerable<>).MakeGenericType(dataType);
    var enumerableParam = Expression.Parameter(enumerableType, "ExtractedCollection");

    var getEnumeratorFunc = Expression.Call(enumerableParam, enumerableType.GetMethod("GetEnumerator"));
    var getEnumeratorLambda = Expression.Lambda(getEnumeratorFunc, enumerableParam);

    var t1 = Expression.Assign(listVariable, Expression.Invoke(getListLambda, typeParam));
    var t2 = Expression.Assign(enumerator, Expression.Invoke(getEnumeratorLambda, listVariable));


    var @break = Expression.Label();

    var funcBlock = Expression.Block(
        new ParameterExpression[] { listVariable, enumerator},

   t1,
   t2,

    Expression.Loop(
        Expression.IfThenElse(

            Expression.NotEqual(Expression.Call(enumerator,typeof(IEnumerator).GetMethod("MoveNext")),Expression.Constant(false)),
                                Expression.Invoke(enumerableExpressions[0],Expression.Property(enumerator, "Current")),

                      Expression.Break(@break))
            , @break), typeParam);



    Expression<Action<TestObject>> lm = Expression.Lambda<Action<TestObject>>(funcBlock,recordExpression);
    var d = lm.Compile(); **//this is exceptioning with " variable 'Input' of type 'TestObject' referenced from scope '', but it is not defined**

Answer 1

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public static Expression ForEach(Expression collection, ParameterExpression loopVar, Expression loopContent)
{
    var elementType = loopVar.Type;
    var enumerableType = typeof(IEnumerable<>).MakeGenericType(elementType);
    var enumeratorType = typeof(IEnumerator<>).MakeGenericType(elementType);

    var enumeratorVar = Expression.Variable(enumeratorType, "enumerator");
    var getEnumeratorCall = Expression.Call(collection, enumerableType.GetMethod("GetEnumerator"));
    var enumeratorAssign = Expression.Assign(enumeratorVar, getEnumeratorCall);

    // The MoveNext method actually on IEnumerator, not IEnumerator<T>
    var moveNextCall = Expression.Call(enumeratorVar, typeof(IEnumerator).GetMethod("MoveNext"));

    var breakLabel = Expression.Label("LoopBreak");

    var loop = Expression.Block(new[] { enumeratorVar },
        enumeratorAssign,
        Expression.Loop(
            Expression.IfThenElse(
                Expression.Equal(moveNextCall, Expression.Constant(true)),
                Expression.Block(new[] { loopVar },
                    Expression.Assign(loopVar, Expression.Property(enumeratorVar, "Current")),
                    loopContent
                ),
                Expression.Break(breakLabel)
            ),
        breakLabel)
    );

    return loop;
}

, , ParameterExpression, , .

, , ...

var collection = Expression.Parameter(typeof(List<string>), "collection");
var loopVar = Expression.Parameter(typeof(string), "loopVar");
var loopBody = Expression.Call(typeof(Console).GetMethod("WriteLine", new[] { typeof(string) }), loopVar);
var loop = ForEach(collection, loopVar, loopBody);
var compiled = Expression.Lambda<Action<List<string>>>(loop, collection).Compile();
compiled(new List<string>() { "a", "b", "c" });

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---

, , for:

public static Expression For(ParameterExpression loopVar, Expression initValue, Expression condition, Expression increment, Expression loopContent)
{
    var initAssign = Expression.Assign(loopVar, initValue);

    var breakLabel = Expression.Label("LoopBreak");

    var loop = Expression.Block(new[] { loopVar },
        initAssign,
        Expression.Loop(
            Expression.IfThenElse(
                condition,
                Expression.Block(
                    loopContent,
                    increment
                ),
                Expression.Break(breakLabel)
            ),
        breakLabel)
    );

    return loop;
}

, :

for (loopVar = initValue; condition; increment)
{
    loopContent
}

, loopContent, condition increment - , loopVar, loopVar .