Why can't String.Empty be used when creating a const string variable?

Question

I often use String.Empty for a placeholder, which equates to "". So my question, why does a const not like String.Empty? They compile identically.

// Good
private const string example = "";

// Bad
private const string example = String.Empty;

What in String.Empty makes it not able to be used with a const.

I would suspect it's because Empty isn't itself a constant, so as far as the compiler is concerned it could resolve to anything. And a const needs to guarantee at compile time what it's value will be. The literal "" provides that guarantee. — David
– David, Commented Aug 9, 2016 at 19:17
@Greg As far as the compiler is concerned, any string value. It has no idea at compile time. — Servy
– Servy, Commented Aug 9, 2016 at 19:17
@Lucas There are millions of ways to subtly break code when you have a malicious developer. String.Empty is no exception to this; a malicious developer could just as easily edit the string that it refers to to a non-empty string (yes, it would absolutely be possible, even through managed code). There's virtually no way to defend code against a malicious developer editing the source code; it's not even something you can meaningfully attempt to defend against. — Servy
– Servy, Commented Aug 9, 2016 at 19:27
Discussion about preferences between String.Empty vs. ""... This question seem to be just about "why readonly can't be use as const" (approximately stackoverflow.com/questions/755685/static-readonly-vs-const) OR "why String.Empty is not const". Some clarification from Greg may help. — Alexei Levenkov
– Alexei Levenkov, Commented Aug 9, 2016 at 20:04

Dmitrii Bychenko · Accepted Answer · 2016-08-09 19:23:13Z

9

String.Empty is not a constant it's only readonly field. And since it's readonly field (which is not known on compile time) it can't be assigned to a constant.

http://referencesource.microsoft.com/#mscorlib/system/string.cs,c9f70a27facb27cf

...
//We need to call the String constructor so that the compiler doesn't mark this as a literal.
//Marking this as a literal would mean that it doesn't show up as a field which we can access 
//from native.
public static readonly String Empty;

edited Aug 9, 2016 at 19:23

answered Aug 9, 2016 at 19:21

Dmitrii Bychenko

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