Comparison of struct with Nullable member

[Nicholas Wilson via Digitalmars-d-learn]

On Friday, 17 July 2015 at 12:18:56 UTC, TC wrote:
> Hello,
> I came around a strange behavior and I'm not sure if it is a 
> bug or feature.
>
> import std.typecons : Nullable;
> struct Foo
> {
> 	string bar;
> 	Nullable!int baz;
> }
>
> auto a = Foo("bb");
> auto b = Foo("bb");
> assert(a == b);
>
> This ends up with: Called `get' on null Nullable!int
>
> But if I change bar to be an int for example, than it passes ok.
> I would expect this to pass ok.
>
> Tested on dmd 2.067.1 win64

what is happening is the complier generated default opEquals is 
accessing the payload for Nullable!T without checking for null 
(which as you've written `Foo("bb")` this constructs a and b as 
`Foo("bb",(Nullable!int).init)` i.e. in the null state)

why nullables don't automatically check for null when comparing 
for equality idk.

you can make this work by defining your own opEquals that 
explicitly checks for nulls.