Optional Method Arguments on byte array

Question

How would i make a default value for a byte array argument? The code below wont work...

public static void init(SomeByteArray[] = {1, 2, 3, 4}) {
    //Do Something
}

Is this possible?

Im doing this in .Net Micro Framework 4.1, if it makes any difference...

Karissakarita

Unfortunately, you can't, as all optional arguments need to be compile-time constants. – Shakedown

Answer 1

From MSDN:

A default value must be one of the following types of expressions:

• a constant expression;
• an expression of the form new ValType(), where ValType is a value type, such as an enum or a struct;
• an expression of the form default(ValType), where ValType is a value type.

So an array instance cannot be used as default value.

The best solution is probbaly two define two overloads as follows:

public static void Init()
{
    Init(new byte[] { 1, 2, 3, 4 });
}

public static void Init(byte[] data)
{
    ...

Brittan

This also has the slight advantage that you can make it invalid for the caller to pass a null to init(), while still having the ability to use a default by omitting the parameter. I'd definitely go with this one myself. – Axseed

Answer 2

You can, but it needs to be assigned in the method, and the default value has to be null, like this:

public static void init(byte[] SomeByteArray = null)
{
    SomeByteArray = SomeByteArray ?? new byte[] {1, 2, 3, 4};
    //carry on with your method.
}

Urbanity

You need to specify byte explicitly as new bye[] {1, 2, 3, 4}, or it's treated as an int array. The peers rejected my revision for that. – North

Answer 3

You can't do that. Default parameters must be compile-time constants, and unfortunately arrays are not.

However, you could do this:

public static void init(byte[] SomeByteArray = null) {
    SomeByteArray = SomeByteArray ?? new byte[] { 1, 2, 3, 4 };
    // Do Something
}

Or this:

public static void init() {
    init(new byte[] { 1, 2, 3, 4 });
}

public static void init(byte[] SomeByteArray) {
    // Do Something
}

Lonergan

@newStackExchangeInstance oops, yes, exactly – Lonergan

Would be the same with init(byte[] SomeByteArray) – Lu

@Lu No it wouldn't, because you'd have to type in null then. – Shakedown

I would personally suggest the same code as the former shows. – North

I get "operator ?? cannot be applied to operands of type byte[] and int[]" – Karissakarita

@ChristianBekker Oops, I guess you need to specify the array type in this case. See my updated answer. – Lonergan

Answer 4

Try:

public class MyClass {
    private readonly int[] _default = new[] { 1, 2, 3, 4 }; 

    public static void init(int[] myArray = null) {
        if (myArray == null) {
            // Don't modify _default to ensure thread safe
            myArray = _default;
        }

        //Do Something
    } 
} 

Rill

You got it wrong there, you're assigning null instead of checking if it is null. Fixing it for you :) – Shakedown

Thanks @Ken and newStackExchangeInstance - whoops! – Rill