The D standard library is built on GC, is that a negative or positive?

[bachmeier]

On Thursday, 15 December 2022 at 23:29:55 UTC, Steven 
Schveighoffer wrote:
> On 12/15/22 6:04 PM, bachmeier wrote:
>> On Wednesday, 14 December 2022 at 01:47:29 UTC, Steven 
>> Schveighoffer wrote:
>> 
>>> But if the string you give it happens to not contain a string 
>>> representation of an integer, it wants to throw an exception. 
>>> And the act of allocating and throwing that exception needs 
>>> the GC.
>>>
>>> We really really need to fix it. It completely cuts the legs 
>>> out of the answer "if you don't want the gc, use @nogc". If 
>>> we do fix it, all these questions pretty much just go away. 
>>> It goes from something like 20% of phobos being 
>>> nogc-compatible to 80%.
>> 
>> Is avoiding the GC inside exceptions a problem that needs to 
>> be solved? Maybe it is, but I don't think it's common to have 
>> a loop with millions of exceptions. Perhaps the issue is that 
>> there should be a version of @nogc that doesn't care about 
>> exceptions. With the current implementation of exceptions, the 
>> intersection of "avoiding GC" and "abusing exceptions" is 
>> almost certainly small.
>
> Why does the quantity of exceptions matter? The point of 
> avoiding the GC is to avoid the collection, which can happen 
> with a single allocation. If you want to avoid the GC for 
> specific code paths, you don't want to say "OK, I guess I can't 
> parse integers in here".

It matters if you expect the quantity to be zero. If you've 
thoroughly tested your code, and you're confident that the 
exception isn't relevant, it doesn't matter. It is quite rare 
that `to!int` would throw an exception in my code.

> Note that it's also possible to assume the GC *likely* won't 
> get triggered, because an exception is very unlikely. But 
> having a mechanism to ask the compiler to help prove it, which 
> can't be used, is pretty frustrating.

Those wanting that could continue to use the current @nogc. If 
they're fine with a one in a million chance of a collection, they 
don't need that kind of proof, and they could use @nogc right now 
with the 80% of Phobos you have cited.