Default Value Operator

[MichaelPuckett2]

Allow types to declare default values in the same way we use custom operators today.

Accessing the default value could be something now exposed via property but it could also be a shortcut to an existing property.

Using Nullable<T> for example but not only for Nullable

Currently you can compare or assign with custom operators but you still have to access Value directly.

Using a Nullable<T> for example:

Currently looks a little like this:

TimeSpan? ts1 = new TimeSpan(0, 30, 0);

if (ts1.HasValue) 
{
     Console.WriteLine($"{ts1.Value.Hours}:{ts1.Value.Minutes}:{ts1.Value.Seconds}");
}

Operator might look something like this:

public static default T(Nullable<T> nullable)
{
    return nullable.Value;
}

Now you could access Value with a double dot operator making it easier to read and a bit more common for other types doing the same thing.

TimeSpan? ts1 = new TimeSpan(0, 30, 0);

if (ts1.HasValue) 
{
     Console.WriteLine($"{ts1..Hours}:{ts1..Minutes}:{ts1..Seconds}");
}

[CyrusNajmabadi]

Right now the LDM is considering just allowing you to write things like ts1.Hours and having that be lifted automatically. So this would be superfluous with that approach.

[MichaelPuckett2]

Can you send the link to those details? I'm curious how this is going to be achieved; which I believe is a good idea; but if it's only for Nullable<T> then I feel like it's not getting us far.

[CyrusNajmabadi]

but if it's only for Nullable then I feel like it's not getting us far.

What other scenarios are do you need this for? Can you update the OP with those examples?

[yaakov-h]

I assume you're referring to #1865?

[MichaelPuckett2]

@CyrusNajmabadi I am the OP... but yes I'll update the proposal with others. I have mocked up examples but didn't want to clutter it up. Having Nullable<T> return the inner type by default was not the goal... The goal was to allow any Type to have the ability to add a default value operator.

[MichaelPuckett2]

@yaakov-h No, that's not the proposal. Maybe I shouldn't have used Nullable<T> for my example but it's the most obvious and talked about; it satisfies that situation as well.

[dsaf]

Would that work with structs?

[orthoxerox]

@dsaf structs are less of a problem, since separate specialized methods are compiled for struct generic parameters. I'm more worried about default(T) on a reference type, since it get's compiled into a null for all reference types.

[Thaina]

@CyrusNajmabadi

Right now the LDM is considering just allowing you to write things like ts1.Hours and having that be lifted automatically. So this would be superfluous with that approach.

Is it possible to did that lifting with Task<T> ?

[Thaina]

@MichaelPuckett2 Actually I think what you want is #889