Wrong statement double.TryParse out parameter might not be initialized?

Question

If wonder why the compiler does not allow me to write the following:

if (someCondition && double.TryParse(astring, NumberStyles.Any, CultureInfo.InvariantCulture, out double v))
{
    // CS0165   Use of unassigned local variable 'v'
    // Seems incorrect, evaluating the conditions will never leave the variable unassigned
}

While it's perfectly fine to write

if (double.TryParse(astring, NumberStyles.Any, CultureInfo.InvariantCulture, out double v))
{
    // No compiler warning, the out parameter is always set
}

Why does the compiler not allow me to write the first example?

update

the input was a string, but was stored in a dynamic property. Damien_The_Unbeliever already pointed out the question which already explains what this means.

if `someCondition` is false the second part won't be executed at all... — Johnny, Oct 16 '19 at 12:39
Is `dynamic` involved anywhere near here? There's a gotcha if the compiler doesn't know whether custom operator true and false might be in play. — Damien_The_Unbeliever, Oct 16 '19 at 12:39
Inside the `if`, `v` is definitely assigned. *Outside* the `if`, it's assigned only if `someCondition` was `true`, which is not definitive. — Jeroen Mostert, Oct 16 '19 at 12:40
Here's the [old question with dynamic in play](https://stackoverflow.com/questions/52541845/bug-with-detection-of-unassigned-local-variables-when-dynamic-variables-affect) — Damien_The_Unbeliever, Oct 16 '19 at 12:41
Use & instead of && to ensure the TryParse() method runs as well. — Hans Passant, Oct 16 '19 at 12:41
My guess is that the variable is being used after the if-statement block as well, which is actually triggering the problem. However, I've only tested this using C# 8 in .NET Core 3, if there's any differences between this and earlier compilers that might also be a factor. — Lasse V. Karlsen, Oct 16 '19 at 12:43
@Damien_The_Unbeliever, I think you nailed it. The answer is yes.... — bas, Oct 16 '19 at 12:43
A quick test in LinqPad (using bool and string variables) shows no complaints — Hans Keﬆing, Oct 16 '19 at 12:45
Please post a full [mcve], so that we can see all the moving bits involved. — Lasse V. Karlsen, Oct 16 '19 at 12:46

Wrong statement double.TryParse out parameter might not be initialized?

update

0 Answers0