On Tue, Aug 19, 2014 at 7:22 PM, John Cowan <co...@mercury.ccil.org> wrote: > Alan Watson scripsit: > >> If I understand correctly, when the first element is assigned to the >> new vector, surely the implementation would have to clear the bit and >> initialise the other elements? > > That would be the safe thing, yes, but R7RS does not explicitly require either > safety or unsafety. I would not want to standardize anything that can't be > made safe, but an unsafe implementation that can only be used in limited > ways (viz. you are not allowed to gc the source vector until the destination > vector is fully initialized) isn't necessarily unusable.
I don't think this is an operation useful enough to spend brain cycles on possible ways to optimize it. But, if we really need this, here's my proposal: (make-vector-from-pieces dim default init...) where each of the inits specifies a range to be filled in the new vector, and an existing vector with a starting point, to be copied in that range. Ranges not included in any /init/ will be initialized with /default/, as in make-vector. This function can be implemented trivially in any Scheme, and an implementor can supply a version for his implementation which avoids double assignments in the newly created vector, and is also safe. P. _______________________________________________ Scheme-reports mailing list Scheme-reports@scheme-reports.org http://lists.scheme-reports.org/cgi-bin/mailman/listinfo/scheme-reports
