I'm guessing you're referring to the fact that the most popular GC languages allocate almost every object on the heap, even when used as a field of another obje

I'm guessing you're referring to the fact that the most popular GC languages allocate almost every object on the heap, even when used as a field of another object. This is by no means a constraint of the GC, it is a separate design choice. And in fact C# has always supported "value objects", which do get allocated in-place, Java is adding the same support probably in the next release, and Go actually defaults to it.