persistent byLine

[monarch_dodra]

On Monday, 22 July 2013 at 23:28:46 UTC, Jonathan M Davis wrote:
> On Monday, July 22, 2013 13:08:05 Nick Treleaven wrote:
>> Hi,
>> I remember an example in some slides by Walter which had this 
>> snippet
>> (slightly simplified):
>> 
>> stdin.byLine.map!(l => l.idup).array
>> 
>> Someone commented in a reddit post that the idup part was not 
>> intuitive
>> (can't find the link now, sorry).
>> 
>> I made a pull request to re-enable using byLine!(char, 
>> immutable char).
>> (Note this compiled in the current release, but didn't work 
>> properly
>> AFAICT. It did work by commit 97cec33^).
>> 
>> https://github.com/D-Programming-Language/phobos/pull/1418
>> 
>> Using that allows us to drop the map!(l => l.idup) part from 
>> the above
>> snippet. The new syntax isn't much better, but it can also be 
>> more
>> efficient (as it caches front). I have an idea how to improve 
>> the
>> syntax, but I'll omit it for this post.
>
> I agree with monarch in that we really shouldn't try and mess 
> with byLine like
> this. It would just be cleaner to come up with a new function 
> for this, though
> I confess that part of me thinks that it's better to just use 
> map!(a =>
> a.idup)(), because it avoids duplicating functionality. It is 
> arguably a bit
> ugly though.

It is also inefficient, if you pipe it to an algorithm that calls 
the same front more than once, you'll end up duping more than 
once. It could be mitigated with my proposed "cache" adaptor, but 
then, we'd have:
file.byLine().map!(a => a.idup)().cache();

It works, but it is horrible to look at.

I'm rather in favor of a named "byDupLine", which is self 
documenting, easy to use, and new/casual programmer friendly.