if (!this) is allowed?

[Александр Гурьянов]

Hi, I have a big code base that uses this pattern:

```

int String::intValue() const {
    if (!this) {
        return 0;
    }
    
   // ...
}

int count = dict->stringForKey("count")->intValue();

```

If dict->stringForKey returns nullptr then wasm is crashed, but native works fine.
This code also worked fine with old versions of emscipten.

I understand that this is ugly pattern, but I am curious if it can work as before?

[Thomas Lively]

I’m pretty sure that calling a method on a null pointer is undefined behavior. My guess is that at some point LLVM started recognizing and optimizing away this UB, which is why you’re seeing different behavior with newer versions of Emscripten.

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[Sam Clegg]

Reminds me of why `this` should really be a reference and not a pointer: https://www.stroustrup.com/bs_faq2.html#this

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[Floh]

Godbolt is great for checking stuff like this:

https://www.godbolt.org/z/vj1q6e

Clang should give a warning (even without evelated warning level), and the undefined behaviour sanitizer also complains.

Since this is C++ anyway (not C), I've seen a nice solution for this type of stuff in TinyXML2, a special special pointer wrapper class which allows safe method chaining, see here:

http://www.grinninglizard.com/tinyxmldocs/classTiXmlHandle.html