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Linq ForEach - Returning cannot assign 'void' to implicitly typed local variable

I am trying to use linq query to save multiple lines of code. I am getting compilation error when I am told:

Returning cannot assign 'void' to an implicitly typed local variable.

var GIANTLIST = new List<string>();

var taskIds = Complaint.Tasks.Select(s => s.Task_ID).ToList().ForEach( s =>
{
    GIANTLIST.Add("<Task_ID=" + s.ToString() + ">");
});

I am trying to understand the linq query better. I understand it got a "void" return type? If so, how can I then add to the list?

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5 answers


Foreach returns no result; you cannot assign it to a variable. Remove var taskIds:

var GIANTLIST = new List<string>();

Complaint.Tasks.Select(s => s.Task_ID).ToList().ForEach( s =>
{
    GIANTLIST.Add("<Task_ID=" + s.ToString() + ">");
});

You have Microsoftsoft documentation here https://msdn.microsoft.com/en-us/library/bwabdf9z%28v=vs.110%29.aspx



I am trying to understand the linq query better. I understand this is getting an "invalid" return type? If so, how can I then add to the list?

Think of it as a ForEach like a normal functional ForEach ForEach (var a in MyList) that it doesn't return anything is also invalid. Inside ForEach, you can directly modify the variables of your classes.

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that ForEach is not part of Linq, it is a method of the List class

keep it simple

var GIANTLIST = Complaint.Tasks.Select(s => "<Task_ID=" + s.Task_ID + ">").ToList();


if you need to add items to an existing list use AddRange instead of ForEach

GIANTLIST.AddRange(Complaint.Tasks.Select(s => "<Task_ID=" + s.Task_ID + ">"));
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The ForEach method returns void. You are assigning to a void

value taskIds

. If you want to fill in taskIds, do the following:

            var GIANTLIST = new List<string>();
            var taskIds = new List<int>();
            Complaint.Tasks.Select(s => s.Task_ID).ToList().ForEach( s =>
            {
                taskIds.Add(s.TASK_ID);
                GIANTLIST.Add("<Task_ID=" + s.ToString() + ">");
            });
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Your attempt to do two things at the same time. Selecting a Task_ID to a list and adding each Task_ID to a different list.

You can do this in two steps

        var GIANTLIST = new List<string>();

        var taskIds = Complaint.Tasks.Select(s => s.Task_ID).ToList();

        taskIds.ForEach(s =>
        {
            GIANTLIST.Add("<Task_ID=" + s.ToString() + ">");
        });

or pre-initialize both lists in advance and add values ​​to ForEach

        var GIANTLIST = new List<string>();
        var taskIds = new List<int>();

        Complaint.Tasks.Select(s => s.Task_ID).ForEach(s =>
        {
            taskIds.Add(s);
            GIANTLIST.Add("<Task_ID=" + s.ToString() + ">");
        });

ForEach itself doesn't return anything, it just performs the specified action for each list object.

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The following should work:

var GIANTLIST = new List<string>();

Complaint.Tasks.Select(s => s.Task_ID).ForEach( s =>
            {
                GIANTLIST.Add("<Task_ID=" + s.ToString() + ">");
            });

or

var GIANTLIST = new List<string>();

 var taskIds = Complaint.Tasks.Select(s => s.Task_ID)

taskIds.ForEach( s =>
                {
                    GIANTLIST.Add("<Task_ID=" + s.ToString() + ">");
                });

You don't actually need to convert ToList()

, ForEach can be called on the base class IEnumerable

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