Is it possible in C# 4.0 method default values parameters as array (for ex. string[] sArray)? if yes, how to implement it?
I tried call function like below:
MethodA(string[] legends=new string[]{"a","b"},float[] values=new float[]{1,2}, string alt="sd");
It's not work
Default values must be compile-time constant, which means arrays cannot be used.
The standard (pg 312) says this:
The expression in a default-argument must be one of the following:
- a constant-expression
- an expression of the form new S() where S is a value type
- an expression of the form default(S) where S is a value type
As others have said, default values can't be arrays. However, one way of avoiding this is to make the default value null and then initialize the array if necessary:
public void Foo(int[] x = null)
{
x = x ?? new int[] { 5, 10 };
}
Or if you're not going to mutate the array or expose it to the caller:
private static readonly int[] FooDefault = new int[] { 5, 10 };
public void Foo(int[] x = null)
{
x = x ?? FooDefault;
}
Note that this assumes null isn't a value that you'd want to use for any other reason. It's not a globally applicable idea, but it works well in some cases where you can't express the default value as a compile-time constant. You can use the same thing for things like Encoding.UTF8 as a default encoding.
If you want a value type parameter, you can just make that a nullable one. For example, suppose you wanted to default a parameter to the number of processors (which clearly isn't a compile-time constant) you could do:
public void RunInParallel(int? cores = null)
{
int realCores = cores ?? Environment.ProcessorCount;
}