Express "Class argument may not be null" ?

[Johan via Digitalmars-d-learn]

On Wednesday, 9 August 2017 at 12:47:49 UTC, Steven Schveighoffer 
wrote:
> On 8/8/17 3:59 PM, Johan Engelen wrote:
>> 
>> In C++, it is clear that the _caller_ is doing the 
>> dereferencing, and the dereference is also explicit.
>
> In fact it's not doing any dereferencing. It's just under the 
> hood passing a pointer.

Come on Steven, I thought you knew I am a compiler dev.

The caller _is_ doing dereferencing. That's what the '*' means 
semantically and it matters. [1]

>>> However, the in contract does actually enforce the 
>>> requirement.
>> 
>> And adds null pointer checks even when clearly not needed.
>
> Clearly not needed? I thought the point was to ensure the 
> reference is not null?

I meant code like this: `k->something(); foo(*k);` or `auto k = 
new Klass(); foo(*k);`.

Anyway, the point was to express the intent nicely.
I wasn't expecting having to explain the merits of passing by 
reference.

- Johan


[1] Going off-topic.
The alternative is dereferencing inside the callee (which is 
apparently the only option D semantically provides for classes). 
I showed the impact of this semantic difference in my DConf 2017 
talk; here are links to  examples:
https://godbolt.org/g/rgvHTC  (C++)
https://godbolt.org/g/NCTeXo  (D)
It's a pity we are not able to pass classes "by reference" (per 
C++ parlance), for reasoning and readability, and performance. I 
still have to come up with a rationale for not having an explicit 
"*" for classes for when I am going to teach D.