How to assign TimeSpan with a default value when using it as an argument?

Question

This does not work:

public void DoStuff(TimeSpan interval = TimeSpan.FromSeconds(5))

The compiler error is: "Error 1 Default parameter value for 'interval' must be a compile-time constant".

I have tried making a const field in the class but still no luck.

Vulpes · Answer

Incidentally whilst it's not appropriate here if you wanted a TimeSpan parameter with a default value of 0 seconds you could simply do this: public static void DoStuff(TimeSpan interval = default(TimeSpan)) { // code } This works because default(TimeSpan) sets all bits to zero and so is equivalent to TimeSpan.Zero. However the former is regarded as a constant but the latter is not.

Vulpes · Answer

Although it's not possible to produce a TimeSpan value which is a compile-time constant you can get around this by using a nullable TimeSpan instead which can take the constant value 'null': public void DoStuff(TimeSpan? interval = null) { if (interval == null) interval = TimeSpan.FromSeconds(5); TimeSpan ts = (TimeSpan)interval; // convert to non-nullable TimeSpan // rest of code } So this call will set 'interval' (and hence 'ts') to 5 seconds: DoStuff(); A similar technique can be used for other structs which lack constant values such as DateTime.

John Penn · Answer

You could pass the interval to DoStuff() and then DoStuff could create the TimeSpan instance internally.

Benjamin Kemner · Answer

Hm that's tricky but I think the only way is to use the constructor argument for default value like this: public void DoStuff(int initvalue=5){ TimeSpan interval = TimeSpan.FromSeconds(initvalue); } Or the old-school way: public void DoStuff(){ DoStuff(TimeSpan.FromSeconds(5)); } public void DoStuff(TimeSpan interval){ }

Zoran Horvat · Answer

First solution: Do not use TimeSpan as argument but integer which receives seconds then declare the method like this: public void DoStuff(int seconds=5) { TimeSpan interval = TimeSpan.FromSeconds(seconds); ... } Second solution: Do it old style C# - define two methods one receiving interval another without arguments: public void DoStuff(TimeSpan interval) { ... } public void DoStuff() { DoStuff(TmeSpan.FromSeconds(5)); } Zoran

Vulpes · Answer

It's not an object it's just a value. So the memory location for TimeSpan.Zero actually contains an 8 byte value - it doesn't contain a reference (i.e. a pointer) to where an instance is stored on the heap which would be the case if TimeSpan were a class rather than a struct. By always calling TimeSpan.Zero you're re-using the value stored at its memory location. This value will persist throughout the application's lifetime and will never be garbage collected.

time and space · Answer

Isn't it generally considered bad to be creating objects during a game loop though? I thought it was best practice to reuse a pool of objects that had been created before hand?

Vulpes · Answer

There would be no point. You'd just be copying the values to another location and it would be no shorter to write.

time and space · Answer

I use TimeSpan.Zero and Vector2.Zero quite a lot in my main game loop. I'm just wondering if I should create instances of them as static globals in my globals class and refer to them that way.

Vulpes · Answer

TimeSpan is actually a struct (i.e. a value type) rather than a class. I think that it uses a long integer (8 bytes) to represent TimeSpan values internally so TimeSpan.Zero will be repesented by a long with a value of 0. TimeSpan.Zero is a static readonly field which creates a single TimeSpan instance. The same instance is used each time the field is accessed. Vector2 is also a struct though for some reason Vector2.Zero is a static readonly property rather than a field.

time and space · Answer

Sorry to bump this old topic but I just wanted to check something. With regards to TimeSpan.Zero does that create a new instance of a TimeSpan object? I guess this question applies to all objects with Zero properties (e.g. Vector2.Zero).

time and space · Answer

Thanks for all the suggestions. Plenty of solutions for me to use.

Zoran Horvat · Answer

That's what I said :) Damn and blast concurrent edit.