ref var

[TonyValenti]

Hi C# team,
Ever since the introduction of "out var", I have found myself writing numerous methods that basically test a condition (actual return value) and return a value (out var) all in one step. A constant limitation that I am running into with these methods though, is the ability to specify a default value. I know that I can specify another parameter but that can make calling messy.

Ideally, I would like to be able to do things like:

//TaskID & Total
var TaskCounts = new Dictionary<int, int>();
...
var TaskID = ...;
TaskCounts.TryGetValue(TaskID, ref var total = 0);

Console.WriteLine($"Task {TaskID} has a total of {total}");

I hope someone else finds the concept of ref var useful for when you want to "out var" something conditionally.

[svick]

I don't understand the example. If TryGetValue returns false, you don't use Value, so the default value does not matter.

And when you want to always have a value, you can use ??:

long? personIndex = …;
var value = personIndex ?? 99;
Console.WriteLine(value);

Do you have an example that uses the default value and can't be replaced by ???

[TonyValenti]

I've updated my example.

[svick]

I know that I can specify another parameter but that can make calling messy.

How so?

Compare:

TaskCounts.TryGetValue(TaskID, ref var total = 0);
TaskCounts.TryGetValue(TaskID, out var total, 0);

The second option doesn't look more messy to me.

(Also, if the default you want is default, then you can use code like TaskCounts.TryGetValue(TaskID, out var total) today.)

[jnm2]

Anyhow, I actually prefer

TaskCounts.TryGetValue(TaskID, out var total) ? total : 0