[OT] OT: Null checks.

[Timon Gehr]

On 5/6/25 08:11, Walter Bright wrote:
> D is set up so if you throw an `Exception`, then destructors will run as 
> the stack unwinds. But if you throw an `Error`, you can catch it but the 
> destructors don't run.
> ...

They do.

```d
import std.stdio;

void main(){
     scope(exit) writeln("hi");
     assert(0);
}
```

This still runs even if I mark `main` nothrow. I understand it's not 
guaranteed (which is bad), but I will take anything I can get.

> The reason is that `Error` means the program has entered an invalid 
> state. Nothing in the program can be trusted any more. The program 
> should do as little as possible to close down gracefully.
> ...

"The patient has a light cough. The patient has thereby entered an 
invalid state. The doctors must now do as little as possible before they 
blow up the hospital in order to euthanize the patient and everyone else 
that may have been in contact with them."

I want to diagnose and heal the patient!

> The template `std.exception.enforce` works like `assert`, but throws an 
> `Exception` instead.
> 
> The documentation for `enforce()` says:
> 
> $(NOTE `enforce` is used to throw exceptions and is therefore intended to
> aid in error handling. It is $(I not) intended for verifying the logic
> of your program - that is what `assert` is for.)
> ...

Oh I know. I am still going to use `enforce` to verify the logic of my 
program. Why? Because the language becomes hostile to your program once 
it can tell anything went wrong. I just want to fix or work around the 
bug and move on.

> What you can do is override the default assert behavior by inserting 
> your own assert handler by calling `core.exception.assertHandler()`. Be 
> sure to set `-checkaction=D`
> 
> Then you can have assert() behave however you want.

Well, I just don't want any hard crashes in production. Druntime throws 
other kinds of errors besides assert errors, by the way.