[m-rev.] for review: Add string indexing predicates that indicate a code unit was replaced.
jfischer at opturion.com
Fri Nov 15 20:42:47 AEDT 2019
On Fri, 15 Nov 2019, Peter Wang wrote:
> On Fri, 15 Nov 2019 17:21:59 +1100 (AEDT), Julien Fischer <jfischer at opturion.com> wrote:
>>> diff --git a/library/string.m b/library/string.m
>>> index a9fbfd693..a28c33792 100644
>>> --- a/library/string.m
>>> +++ b/library/string.m
>>> @@ -262,6 +262,10 @@
>>> % Reading characters from strings.
>>> +:- type maybe_replaced
>>> + ---> not_replaced
>>> + ; replaced_code_unit(uint8).
>> Document that type.
>> Is there a reason you didn't have the predicates below return a single
>> value? (i.e. a value that's either a character in the string of the
>> invalid code unit)
> As in
> :- type char_or_replaced
> ---> char(char)
> ; replaced_code_unit(uint8).
> :- pred index_next_repl(string::in, int::in, int::in,
> char_or_replaced::out) is semidet.
> I forgot to consider it.
> Using two return values has an advantage in that it avoids memory
> allocation in the normal case. That advantage should go away once the
> necessary argument packing optimisations are turned on.
> The argument packing wouldn't be used for Java/C#.
At least as they are now ...
> The Java backend needs to allocate an array to return two values,
> so maybe there is no difference there.
> But the C# backend will not need to allocate an object to hold the char.
> (I didn't measure anything; maybe none of this matters.)
It doesn't particularly matter, I was just curious.
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