Does C# 6 Elvis operator (null propagation) short circuit

Question

Why this c# code throws a null exception?

bool boolResult = SomeClass?.NullableProperty.ItsOkProperty ?? false;

Isn´t elvis operator supposed to stop evaluation (short circuit) once the NullableProperty evaluates to null?

In my understanding the line of code above is a shortcut for:

bool boolResult 
if(SomeClass != null)
    if(SomeClass.NullableProperty != null)
        boolResult = SomeClass.NullableProperty.ItsOkProperty;
    else
        boolResult = false;
else
    boolResult = false;

Did I assume wrong?

EDIT: Now I understand why I get it wrong, The line of code actually translates to something similar to:

bool boolResult 
if(SomeClass != null)
    boolResult = SomeClass.NullableProperty.ItsOkProperty;
else
    boolResult = false;

And throws because NullableProperty is null...

Ah, I think what you wanted was `SomeClass?.NullableProperty?.ItsOkProperty` — , Jun 10 '15 at 19:08

score 9 · Accepted Answer · answered Jun 10 '15 at 19:08

9

You need to chain, since the NRE is on the second reference:

bool boolResult = SomeClass?.NullableProperty?.ItsOkProperty ?? false;

answered Jun 10 '15 at 19:08

Mark Brackett

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does the result need to be nullable? i.e. bool? – NeddySpaghetti Jun 11 '15 at 06:08
The ?? operator at the end performs conversion to false if the result of the left-hand operator is null, therefore the result will always be true or false. – Ferazhu Apr 17 '22 at 22:28

Does C# 6 Elvis operator (null propagation) short circuit

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