Why does ConcurrentDictionary.TryRemove require a second out argument?
I only want to remove a value.. I don't need to use the variable afterwards. Why not include an overload where this second parameter was not required?
Do I really have to just store it in a temporary local variable, not use it, and have the garbage collector collect it when the method ends? Seems rather silly..
The function开发者_开发技巧: http://msdn.microsoft.com/en-us/library/dd287129.aspx
C#7 added discard syntactic sugar
So now you can write:
dictionary.TryRemove(entry.Key, out _);
Reference
We allow "discards" as out parameters as well, in the form of a _, to let you ignore out parameters you don’t care about:
p.GetCoordinates(out var x, out _); // I only care about x
You can create exactly the method you want:
public static class ConcurrentDictionaryEx {
public static bool TryRemove<TKey, TValue>(
this ConcurrentDictionary<TKey, TValue> self, TKey key) {
TValue ignored;
return self.TryRemove(key, out ignored);
}
}
UPDATE: Or, as Dialecticus mentioned in the comments, just use Remove
. But note that, since it's an explicit interface implementation, you'll need a reference to an IDictionary<TKey, TValue>
, which leads you back to creating an extension method if you want to avoid casting a ConcurrentDictionary<TKey, TValue>
reference:
public static class ConcurrentDictionaryEx {
public static bool Remove<TKey, TValue>(
this ConcurrentDictionary<TKey, TValue> self, TKey key) {
return ((IDictionary<TKey, TValue>)self).Remove(key);
}
}
If you're not interested in the value that was removed, simply call IDictionary.Remove(key)
. It's shadowed, so you have to invoke it explicitly.
Example:
var dict = new ConcurrentDictionary<string, string>();
dict.AddOrUpdate("mykey", (val) => "test", (val1, val2) => "test");
((IDictionary)dict).Remove("mykey");
The TryRemove(key, out value)
method is there to give you feedback whether the operation made any change. Use the one that best suits your needs.
I believe the 2nd argument is required is because you may need to do something with the item that you're removing from ConcurrentDictionary
.
For example, imagine you have a ConcurrentDictionary<int, MyDisposable>
where MyDisposable
implements IDisposable
. ConcurrentDictionary.TryRemove(...)
doesn't call .Dispose();
on the item being removed from the dictionary.
In the code below, the .Dispose();
call succeeds because the MyDisposable
hasn't been disposed, yet.
void Main()
{
var dict = new ConcurrentDictionary<int, MyDisposable>();
dict.TryAdd(1, new MyDisposable());
dict.TryRemove(1, out var d);
d.Dispose();
}
public class MyDisposable : IDisposable {
#region IDisposable Support
private bool disposedValue = false; // To detect redundant calls
protected virtual void Dispose(bool disposing)
{
if (!disposedValue)
{
if (disposing)
{
// TODO: dispose managed state (managed objects).
}
// TODO: free unmanaged resources (unmanaged objects) and override a finalizer below.
// TODO: set large fields to null.
disposedValue = true;
}
}
// TODO: override a finalizer only if Dispose(bool disposing) above has code to free unmanaged resources.
// ~MyDisposable()
// {
// // Do not change this code. Put cleanup code in Dispose(bool disposing) above.
// Dispose(false);
// }
// This code added to correctly implement the disposable pattern.
public void Dispose()
{
// Do not change this code. Put cleanup code in Dispose(bool disposing) above.
Dispose(true);
// TODO: uncomment the following line if the finalizer is overridden above.
// GC.SuppressFinalize(this);
}
#endregion
}
Now it has an overload that does not out
any parameters:
public bool TryRemove(KeyValuePair<TKey, TValue> item)
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