C#•2y ago

What is this type of Overloading?

I'm converting from vb to c#. What's the correct term for the line public RelayCommand(Action<object> execute) : this(execute, null) in this overloading? It's very helpful:

public class RelayCommand : ICommand
    {
        public RelayCommand(Action<object> execute, Predicate<object> canExecute)
        {
            if (execute == null)
                throw new ArgumentNullException("execute");

            _execute = execute;
            _canExecute = canExecute;
        }

        public RelayCommand(Action<object> execute) : this(execute, null)
        {

        }    
    }

public class RelayCommand : ICommand
    {
        public RelayCommand(Action<object> execute, Predicate<object> canExecute)
        {
            if (execute == null)
                throw new ArgumentNullException("execute");

            _execute = execute;
            _canExecute = canExecute;
        }

        public RelayCommand(Action<object> execute) : this(execute, null)
        {

        }    
    }

10 Replies

Tvde1•2y ago

Constructor overload? Where one constructor calls the other

stigzler•2y ago

hey, thanks for the response. It was more the c# shortcut - i.e. putting the : this(execute,null) on the end, rather than typing RelayCommand(execute, null) in the method body. Having thought about it, maybe it doesn't have a name. I just need to find all these handy c# shortcuts. I thought it might have one as it's similar to the syntax for Inherits where you put a colon after the Class name e.g. : INotifyPropertyChanged

ero•2y ago

it's not a shortcut. it would be impossible to put that into the body

stigzler•2y ago

@Ero ? So replacing

        public RelayCommand(Action<object> execute) : this(execute, null)
        {

        }

        public RelayCommand(Action<object> execute) : this(execute, null)
        {

        }

with

      public RelayCommand(Action<object> execute)
        {
            RelayCommand(execute, null);
        }

      public RelayCommand(Action<object> execute)
        {
            RelayCommand(execute, null);
        }

wouldn't work?

Brady Kelly•2y ago

Nope

stigzler•2y ago

Oh well - I know I'm fgoing to get a null reference exception if that's what you're meaning?

Brady Kelly•2y ago

You just can't call a constructor from within a constructor, it can only be called with new and with the : this(<args>) notation

stigzler•2y ago

ah! Well that I would never have known! Thanks a bunch. What's the best reference for all these types of c# idiosyncrasies? That would have driven me potty if I'd have gotten stuck with that. Is there a site? I've done quite a bit of reading on the basics, but it's stuff like this that's going to catch me out

Brady Kelly•2y ago

I don't know of a resource for all idiosyncracies but you can read up on constructor chaining in C#

stigzler•2y ago

Ha! and that answers the original question. "Constructor Chaining" Thanks again.

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What is this type of Overloading?