Discussion: Add unboxed mutable references somewhere sensible

Dan Doel dan.doel at gmail.com
Thu Feb 12 02:36:20 UTC 2015

We could add something like this to primitive. It has a generalization of
things like STRef, under the name MutVar.

On Wed, Feb 11, 2015 at 7:03 PM, David Feuer <david.feuer at gmail.com> wrote:

> The problem they solve is perhaps not as well known as it should be:
> Code that frequently modifies an `STRef Int`, for example, will
> typically surprise the programmer by allocating a ton of memory. This
> happens because the reference holds a *boxed* Int. Code like
>     modifySTRef ref (+1)
> will allocate a new Int box every time. To the best of my knowledge,
> GHC makes no attempt to figure out if this is actually necessary and
> do something about it. The Data.Ref.Unboxed module in the ArrayRef
> package attempts to address this, but it doesn't seem to get much
> visibility, and its code hasn't been touched since 2009. What can we
> do about this?
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