C# – Understanding the Coalesce Operator

.netasp.netc++null-coalescing-operator

I think i remember seeing something similar to the ?: ternary operator in C# that only had two parts to it and would return the variable value if it wasn't null and a default value if it was. Something like this:

tb_MyTextBox.Text = o.Member ??SOME OPERATOR HERE?? "default";

Basically the equivalent of this:

tb_MyTextBox.Text = o.Member != null ? o.Member : "default";

Does such a thing exist or did I just imagine seeing this somewhere?

Best Answer

Yup:

tb_myTextBox.Text = o.Member ?? "default";

https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/operators/null-coalescing-operator

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C# Coalesce Operator – Usage and Examples

"the left part is simply ignored"? How likely do you really think that is?

Operator precedence dictates that your first version is parsed like so:

bool? result = (someCondition ?? someConditionOverride) 
                   ? false 
                   : (bool?)null;

someCondition isn't null, and it is true. Therefore, this expression evaluates as true:

(someCondition ?? someConditionOverride)

So we get the ? branch, and the whole expression returns false, just like you told it to.

Adding the brackets that you added completely changes the meaning of the expression. It fixes your confusion, in a limited sense, by bringing the actual meaning of the expression in line with your original intent; but the compiler is never confused. In C#, compiler confuses you.

To reduce my own confusion, I never rely on operator precedence. I parenthesize everything. If I had designed the language, the grammar would require it (unless Eric comes by and tells me why that's actually not such a good idea after all, for some reason that will make perfect sense to me once Eric explains it).

UPDATE: Prediction validated: Eric came by and said that too many people would find it ridiculous to have to parenthesize a + b * c, and if you allow that, there's no reasonable way to define the exceptions. Well, if they won't tolerate being forced to parenthesize everything, they won't, however much I think they should.

Best Answer

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C# Coalesce Operator – Usage and Examples

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