[ruby-core:98423] [Ruby master Feature#16899] Add method `Array#both_end`
From:
gamelinks007@...
Date:
2020-05-18 01:44:08 UTC
List:
ruby-core #98423
Issue #16899 has been updated by S_H_ (Shun Hiraoka).
Thanks for feedbacks.
shan (Shannon Skipper) wrote in #note-1:
> I think #both_ends reads better in the plural form. Or #first_last harkens to #min_max and is unambiguous. Other options might be #extremes or #bookends.
>
> I'd vote #first_last.
shevegen (Robert A. Heiler) wrote in #note-2:
> I think #first_last would be a better name as well; primary reason being that we
> already have #first and #last.
>
> I am also ok with the proposal itself, although I think I have not had a need to
> use this often. But I don't mind such a method existing.
>
> #extremes is a bit of a strange name though. It reminds me of mathematics.
>
> #bookends for some reason reminds me of a bookworm - no idea why. :)
>
> #both_end and #both_ends are a bit strange as names. I think one problem here
> is that the name implies "ends", but we also have #first and #last, and I am
> not sure if both first, and last, can be considered as two ends? What about
> circular arrays? :P
>
> So I think #first_last would be a better name. (A single name might be better
> but it is harder to find a goot name there.)
#first_last is good name. I use this name.
shyouhei (Shyouhei Urabe) wrote in #note-5:
> Why not start as a gem? There are things not possible without core changes, but it seems this requested feature needs no such things.
OK, I'll started create gem to Array#first_last and other useful methods implmented.
Thanks.
----------------------------------------
Feature #16899: Add method `Array#both_end`
https://bugs.ruby-lang.org/issues/16899#change-85693
* Author: S_H_ (Shun Hiraoka)
* Status: Open
* Priority: Normal
----------------------------------------
Add a method that gets both the first and the last elements of an array: `Array#both_end`.
## Current Status
Sometimes, we want to get the elements at both ends of an array. But now, no method has this behavior.
So, define this method:
```ruby
class Array
def get_first_and_last(count)
[self.first(count), self.last(count)]
end
end
```
## Proposal
Get the elements at both ends of an array with `Array#both_end`.
Implement a new method `Array#both_end` that gets the elements at both ends of an array.
## Array#both_end behavior
Normal array:
```ruby
ary = [ "w", "x", "y", "z" ]
ary.both_end #=> ["w", "z"]
ary.both_end(2) #=> [["w", "x"], ["y", "z"]
```
Empty array:
```ruby
[].both_end #=> [nil, nil]
[].both_end #=> [nil, nil]
```
Argument exceeds the array size:
```ruby
ary = [ "w", "x", "y", "z" ]
ary.both_end(10) #=> [[ "w", "x", "y", "z" ], [ "w", "x", "y", "z" ]]
```
## Implementation
This implementation uses `Array#asscoc`, `Array#first`, and `Array#last` in C function.
```c
static VALUE
rb_ary_both_end(int argc, VALUE *argv, VALUE ary)
{
VALUE first, last;
rb_check_arity(argc, 0, 1);
if (RARRAY_LEN(ary) == 0)
return rb_assoc_new(Qnil, Qnil);
first = rb_ary_first(argc, argv, ary);
last = rb_ary_last(argc, argv, ary);
return rb_assoc_new(first, last);
}
```
## Problem
I'm wondering if the following code should raise an error, and if so, what kind of error is the best.
Argument exceeds the array size:
```ruby
ary = [ "w", "x", "y", "z" ]
ary.both_end(10) #=> error can't get both end value!
```
I wonder if this method name (`Array#both_end`) is the best.
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