Why can't I use string.Empty as an optional parameter contrary to empty quotation marks? [duplicate]

Question

I'm refining my code and noticed that at some places I had optional parameters with the default value of an empty string. I changed that to a default value from the class for empty string and guess what! Apparently there's a difference between empty quotation marks and string.Empty. What the duck?! (typo intended)

private void Khaboom(String parameter = "") { ... } private void Bazinga(String parameter = String.Empty) { ... }

Can someone explain to me why the duck does Khaboom work while Bazinga doesn't?!

The error message whines this:

Default parameter value for 'parameter' must be a compile-time constant.

Well... It is!

@MichaelPerrenoud Duplicated what?

Konrad Viltersten
– Konrad Viltersten

2014-06-01 22:14:41 +00:00
Commented Jun 1, 2014 at 22:14 — Konrad Viltersten
– Konrad Viltersten, Commented Jun 1, 2014 at 22:14
I marked it as a duplicate but then reopened it.

Mike Perrenoud
– Mike Perrenoud

2014-06-01 22:15:50 +00:00
Commented Jun 1, 2014 at 22:15 — Mike Perrenoud
– Mike Perrenoud, Commented Jun 1, 2014 at 22:15

spender · Accepted Answer · 2014-06-01 22:07:05Z

13

Empty is defined as follows:

public static readonly string Empty

It's not a constant. It's a readonly field.

answered Jun 1, 2014 at 22:07

spender

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6 Comments

Scott DePouw Over a year ago

And for those wondering why it is not a constant, there might actually be a very good reason for that.

spender Over a year ago

@Scott... I did wonder... thx.

Jeppe Stig Nielsen Over a year ago

@Scott Your link gives absolutely no good reason why string.Empty was not chosen to be a const field. The reason is much more obscure. There are threads on this topic here on Stack Overflow.

spender Over a year ago

@JeppeStigNielsen: Where?

Jeroen Vannevel Over a year ago

stackoverflow.com/questions/507923/…

|

Jeroen Vannevel · Accepted Answer · 2014-06-01 22:06:09Z

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.

Since string.Empty is neither of these things, it is not allowed.

http://msdn.microsoft.com/en-us/library/dd264739.aspx

Richard Szalay · Accepted Answer · 2014-06-01 22:07:03Z

2

Default parameter values are required to be constants, but String.Empty is a read only field.

answered Jun 1, 2014 at 22:07

Richard Szalay

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