In this popular question about why substring takes O(n) in C#, one of the main answers provided argued that if a large array were allocated and substrings computed by having the new strings just reference a small slice of the array, the garbage collector would not be able to reclaim the array of characters containing the larger string even if the original string were no longer being referenced.
This seems like a perfectly valid answer, but it seems like in theory one could construct a garbage collector for arrays that allowed for most of an array to be garbage collected while leaving behind some small subarray that's still in use. In other words, if there were a 50,000-element array of which only a small 100-element slice was still in use, the garbage collector could split the array into three pieces - the elements before the 100-element slice, the 100-element slice itself, and the elements after the 100-element slice - and then garbage collect the first and last of these pieces.
My question is whether any language implementations actually use this sort of garbage collector, or whether it exists only in theory. Does anyone know of an example of a language implementation that has an garbage collector like this?