The problem of getting the correct extension method
I am trying to create an AddRange extension method for a HashSet, so I can do something like this:
var list = new List<Item>{ new Item(), new Item(), new Item() };
var hashset = new HashSet<Item>();
hashset.AddRange(list);
This is what I have so far:
public static void AddRange<T>(this ICollection<T> collection, List<T> list)
{
foreach (var item in list)
{
collection.Add(item);
}
}
The problem is that when I try to use AddRange I get this compiler error:
The type arguments for method 'AddRange<T>(System.Collections.Generic.ICollection<T>, System.Collections.Generic.List<T>)' cannot be inferred from the usage. Try specifying the type arguments explicitly.
In other words, I have to use this instead:
hashset.AddRange<Item>(list);
What am I doing wrong here?
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2 answers
Your code works fine for me:
using System.Collections.Generic;
static class Extensions
{
public static void AddRange<T>(this ICollection<T> collection, List<T> list)
{
foreach (var item in list)
{
collection.Add(item);
}
}
}
class Item {}
class Test
{
static void Main()
{
var list = new List<Item>{ new Item(), new Item(), new Item() };
var hashset = new HashSet<Item>();
hashset.AddRange(list);
}
}
Could you please give a similarly short but complete program that won't compile?
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