运行时生成的表达式不能更改字典的值

Question

我正在尝试在运行时创建一些表达式来更改给定字典的值。我创建了这个成功生成表达式并将其编译为 Action 的片段。但是调用动作不能修改字典的值，也不会抛出任何错误。这是代码：

public class ChangeDicValue {

    public void Change(IDictionary<string, object> dic) {
        var blocks = MakeCleaningBlock(dic);
        foreach (var block in blocks) 
            block.Invoke(dic);
    }

    private List<Action<IDictionary<string, Object>>> MakeCleaningBlock(IDictionary<string , object > dic) {

        var allKeys = dic.Keys.ToArray();

        var dicType = typeof(IDictionary<,>).MakeGenericType(typeof(string), typeof(object));

        var dicContainsMethod = dicType.GetMethod("ContainsKey", new[] {typeof(string)})
                                ?? throw new InvalidOperationException();

        var actions = new List<Action<IDictionary<string, Object>>>();

        ParameterExpression actionArguments =
            Expression.Parameter(dicType, "actionArguments");

        foreach (var k in allKeys) {

            Expression key = Expression.Constant(k, typeof(string));

            Expression target = Expression.Property(actionArguments, "Item", key);

            var innerStatements = new List<Expression>(Changers);

            var cleanStatements = new List<Expression>();

            foreach (var ins in innerStatements) {
                var assign = Expression.Assign(target, Expression.Block(ins, target));

                cleanStatements.Add(assign);
            }

            Expression body1 = Expression.Block(new List<Expression>(cleanStatements) {target});

            var callToContains = Expression.Call(actionArguments, dicContainsMethod, key);
            var ifThenBody     = Expression.IfThen(callToContains, body1);

            var cleanedValueBlock = Expression.Block(target, ifThenBody, target);

            var assignDic = Expression.Assign(target, cleanedValueBlock);
            // see the debug view of assignDic in UPDATE

            var lambda = Expression.Lambda<Action<IDictionary<string, Object>>>(assignDic, actionArguments);

            var method = lambda.Compile();

            actions.Add(method);
        }

        return actions;
    }


    private static readonly Expression<Func<object, string>>[] Changers
        = {
            s => s + " First changer added.", 
            s => s + " Second changer added."
        };

}

如您所见，这是一个非常简单的代码，不会导致任何错误。你知道我错过了什么吗？

编辑：

示例字典中一项的变量 assignDic 的调试视图：

$actionArguments.Item["a"] = .Block() {
    $actionArguments.Item["a"];
    .If (
        .Call $actionArguments.ContainsKey("a")
    ) {
        .Block() {
            $actionArguments.Item["a"] = .Block() {
                .Lambda #Lambda1<System.Func`2[System.Object,System.String]>;
                $actionArguments.Item["a"]
            };
            $actionArguments.Item["a"] = .Block() {
                .Lambda #Lambda2<System.Func`2[System.Object,System.String]>;
                $actionArguments.Item["a"]
            };
            $actionArguments.Item["a"]
        }
    } .Else {
        .Default(System.Void)
    };
    $actionArguments.Item["a"]
}

.Lambda #Lambda1<System.Func`2[System.Object,System.String]>(System.Object $s) {
    $s + " First changer added."
}

.Lambda #Lambda2<System.Func`2[System.Object,System.String]>(System.Object $s) {
    $s + " Second changer added."
}

Answer 1

好的。最后我找到了问题和解决方案。代码的断点位于内部 foreach 循环中的赋值，我试图将 Expression.Block 赋值给 IndexerExpression。似乎 blocking 表达式不会调用它。因此，我通过调用 Expression.Invoke 并传递 IndexerExpression（名为 target）将其更改为 InvokationExpression，现在它就像一个魅力：

foreach (var ins in innerStatements) {
    var assign = Expression.Assign(target, Expression.Invoke(ins, target));
    cleanStatements.Add(assign);
}

运行时生成的表达式不能更改字典的值

Runtime generated expression cannot change dictionary's values

c#

.net-core

expression-trees

c#-8.0

.net-core-3.1