I have a method that takes a string[] as parameter, but I am unable to provide it with a default:
void Foo(string[] param = new[]) {
}
complains that the default should be a compile time constant. But what compile time constant is there as an empty array?
I know I can use default, but I was wondering what the syntax was explicitly, if at all possible.
A default value must be compile time value and there are no compile time const arrays in C# and your options are:
default will mean null so you'd have to change string[] to string[]?.
void Foo(string[]? x = default) // OK.
{
}
void Foo(string[] x = default) // Cannot convert null literal to non-nullable reference type.
{
}
To soften the blow you could:
void Foo(string[]? x = default)
{
string[] y = x ?? new string[] {};
// use y below
}
or even:
void Foo() => Foo(new string[] {});
void Foo(string[] a)
{
}
string[] param = null works fine, as does string[] param = default
string[] a = null works with nullable reference types off which in practice is <.NET 6 (C# 10). You said "I don't like null" so I assumed you have nullable reference types on.You can use an optional parameter with the params keyword which allows you to pass a variable number of arguments to the method.
You can refer to this page. https://geeksnewslab.com/how-to-add-a-default-value-for-a-string-array-in-a-method/
params keyword documentation to mitigate that chance.
The default value must be one of the following in C# :
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."
The arrays you created don't follow any of the above rules of C#, and it is a reference type so there can be only one default value which is: null
And one more thing, Array is a reference type, so it initializes by new keyword so anything which initializes by new cannot be constant thus constant of the reference type is null
So You can use = null or = default
void Foo(string[] param = null) {
param = param==null ? new[] : param;
}
OR
void Foo(string[] param = default) {
}
nullto represent an empty array. What kind of default value do you actually need ?nulland prefer Null-objects.default(string[])which is pretty much the same as usingnull. dotnetfiddle.net/TRXdnyvoid Foo(params string[] myArr)