Passing func from method parameter into a LINQ method (generic types)

Question

In the signature of a method I specify a Func, like so:

public void Method (Func<string, bool> func)

In LINQ, which method (from IEnumerable) will let me pass in a Func from the method parameter to the LINQ query? The other issue is, my func can have any type parameter(s) so the Method from IEnumerable/LINQ must support generic type placeholders.

I want to write something like this:

// Get all elements of type T from the webpage (find is an object in an external API to look for elements in a page).

IEnumerable<T> images = find.GetAllByTagName<T>().All(func);

// Where func is a method parameter which is assigned at run time by the consumer of this API:

public void Test (Func<T, bool> func) { }

How can I best do this? I am on .NET 3.5

Thanks

Answer 1

Change your API's signature to be open:

public void Method<T> (Predicate<T> func)

Your consumer would close the generic signature with a type T, and supply an appropriate Predicate.

The actual method implementation using LINQ would use Joel's aforementioned Where()

Edit: changed func to predicate

Additional Edit:

I'd personally return an IEnumerable representing your result set constrained by the predicate passed in:

public IEnumerable Method<T> (Predicate<T> func)
{
    return find.Where(func)
}

I'm making some assumptions of what you're trying to do, let me know if this is your intent.

Answer 2

In LINQ, which method (from IEnumerable) will let me pass in a Func from the method parameter to the LINQ query?

That question is a little fuzzy to me. If you're looking for a filter algorithm that returns only the matches specified by the Func, use the .Where method:

public void Method (Func<string, bool> func)
{
    return find.GetAllByTagName<T>().Where(func);
}

Does that answer your question? If not, please clarify what you're trying to do.

Answer 3

In LINQ, which method (from IEnumerable) will let me pass in a Func from the method parameter to the LINQ query?

The extension methods for LinqToObjects hang out on the static System.Linq.Enumerable class.

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Given your Func signature, you probably want this overload of Enumerable.Where.

IEnumerable<T> Enumerable.Where<T>(this IEnumerable<T> source, Func<T, bool> filter)