Passing some of a LINQ query into an argument of a function?

Question

I have the following code sample in C# demonstrating how I would like to parse some of a LINQ query into a function's argument.

public List<object> AllElements;

public object GetAll<T>(SomeLINQQuery) {

    //get some elements from AllElements where the argument is added to the query, as shown below.

}

And now, to give this some meaning, what I was thinking of accomplishing would be this:

public void test() {
    GetAll<object>(where object.ToString() == "lala");
}

It's kind of hard to explain. I hope this example does it well.

I like that you provide a use-case. If there's a use case, there's usually code that can be written that makes the whole thing work :) — GregC
– GregC, Commented Apr 7, 2011 at 9:24
From your use-case, it's unclear what the returned object is for. — GregC
– GregC, Commented Apr 7, 2011 at 9:25

Daniel Hilgarth · Accepted Answer · 2011-04-07 09:16:20Z

13

Sure. You would do it like this:

public List<T> GetAll<T>(List<T> list, Func<T, bool> where)
{
    return list.Where(where).ToList();
}

You would call it like this:

var result = GetAll(AllElements, o => o.ToString() == "lala");

You could even create it as an extension method:

public static List<T> GetAll<T>(this List<T> list, Func<T, bool> where)
{
    return list.Where(where).ToList();
}

and call it like this:

var result = AllElements.GetAll(o => o.ToString() == "lala");

But really, in your simple example, it doesn't make any sense, because it is exactly the same as using Where directly:

var result = AllElements.Where(o => o.ToString() == "lala").ToList();

However, if your GetAll method does some more stuff, it could make sense to pass the predicate to that method.

edited Apr 7, 2011 at 9:16

answered Apr 7, 2011 at 9:11

Daniel Hilgarth

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2 Comments

GregC Over a year ago

Looks good, but I'd defer the actual execution of the query to the last possible moment by using IEnumerable<T> instead. It's a bad practice to take concrete containers as arguments.

Daniel Hilgarth Over a year ago

I was just reusing his type. I agree, that he should use IEnumerable<T> instead.

LukeH · Accepted Answer · 2011-04-07 09:12:11Z

1

You could pass some sort of predicate to the method:

var query = GetAll(x => x.ToString() == "lala");

// ...

public IEnumerable<object> GetAll(Func<object, bool> predicate)
{
    return AllElements.Where(predicate);
}

answered Apr 7, 2011 at 9:12

LukeH

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2 Comments

Michiel Cornille Over a year ago

So should we use Func<T, bool> like daniel said or Func<object, bool>

LukeH Over a year ago

Well, Daniel's version is more generic and flexible, but since AllElements is a List<object> then Func<object,bool> will suffice.

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