String interpolation, string formatting and null coalescing operator at once

Question

I need this: If the following formatted value is null, display N/A. Otherwise, display the formatted value. It needs to be with string interpolation. I tried to do something like nested interpolation:

$"{$"({someValue:N0})" ?? "N/A" }"

but the result is just empty string. Using .NET 7.

String interpolation will never yield null so the ?? "N/A" part is completely superfluous. — madreflection
– madreflection, Commented Nov 8, 2023 at 21:50
Thanks, it makes sense I guess. Could you suggest an alternative way to format a string with ?? or is it off the table entirely? — ISquared
– ISquared, Commented Nov 8, 2023 at 21:51
Alternative way without interpolation: someValue?.ToString("N0") ?? "N/A" — Ed'ka
– Ed'ka, Commented Nov 8, 2023 at 22:11
@madreflection Well, technically a custom string interpolation handler can do anything, including returning null — Ed'ka
– Ed'ka, Commented Nov 8, 2023 at 23:49
@Ed'ka: Edge case. Technically, you're right because it could yield null in the same way that you can set a non-nullable string to null with !, but I'd say that any interpolated string handler that yields null is broken because it didn't interpolate to a string instance. The interpolated string handlers implemented in the BCL don't yield null. — madreflection
– madreflection, Commented Nov 9, 2023 at 1:10

MediocreFantasy · Accepted Answer · 2023-11-08 21:52:40Z

1

I believe your issue here is that $"({someValue:N0})" will never evaluate to null becasue of the () outside the {}. What I would do here is the following:

(someValue == null ? "N/A" : $"({someValue:N0})"

This is essentially an inline if/else statement, where the portion before the ? is the condition, the first string (before the :) is what you get if the condition is true, and the second string is what you get if the condition is false.

answered Nov 8, 2023 at 21:52

MediocreFantasy

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