copy-instance kwargs to overwrite slots
#827
Conversation
You can now do e.g. `(copy-instance SOME-BINARY-CLASSICAL-INSTRUCTION :left NEW-LEFT-OPERAND)` to make a copy of `SOME-BINARY-CLASSICAL-INSTRUCTION` that has its `left` slot overwritten with `NEW-LEFT-OPERAND`. I suspect there are plenty of places in the QuilC code where this would enable a much nicer functional style by eliminating patterns like `(let ((copy (copy-instance FOO))) (setf (FOO-BAR FOO) BAR))`.
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Neat! I tried writing something like this to chase this same pattern, and I was unhappy about having to treat struct and class instances separately, so it never made it in. Some years older and wiser, I think it’s a good enough idea that it should go in anyway. |
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I think the only way to do this for subclasses of Oh, speaking of which, the default method for ETA: let's all take this as a lesson to prefer |
The "default" method for `copy-instance` is now specialized on `standard-object` rather than `t`. Aside from opening the possibility that it might have been applied to instances of `built-in-class`, the default method's applying to `structure-object`s was non-conformant and SBCL specific (possibly other implementations as well, but certainly not universal), as the MOP as specified in AMOP applies only to `defclass`-defined classes, not to `defstruct` classes. In lieu of a generic implementation for structs, we now use a macro `define-copy-struct-instance` to define methods specific to each `structure-object` subclass. Pros: - More correct; no longer relying on SBCL-specific behavior - Potential modest performance increases, as copying structure objects no longer uses the MOP to dynamically compute a set of slots to copy. Cons: - Ugly, complex macro-ology in `define-copy-struct-instance` - Having to define instances explicitly for structs is frustrating - Potential bugs when a `defstruct` is incompatibly redefined without also editing its corresponding `define-copy-struct-object` form.
You can now do e.g.
(copy-instance SOME-BINARY-CLASSICAL-INSTRUCTION :left NEW-LEFT-OPERAND)to make a copy ofSOME-BINARY-CLASSICAL-INSTRUCTIONthat has itsleftslot overwritten withNEW-LEFT-OPERAND. I suspect there are plenty of places inthe QuilC code where this would enable a much nicer functional style by eliminating
patterns like
(let ((copy (copy-instance FOO))) (setf (FOO-BAR FOO) BAR)).