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Feature #16899

Add method `Array#both_end`

Added by S_H_ (Shun Hiraoka) 3 months ago. Updated 3 months ago.

Status:
Open
Priority:
Normal
Assignee:
-
Target version:
-
[ruby-core:98411]

Description

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:

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:

ary = [ "w", "x", "y", "z" ]
ary.both_end     #=> ["w", "z"]
ary.both_end(2)  #=> [["w", "x"], ["y", "z"]

Empty array:

[].both_end    #=> [nil, nil]
[].both_end    #=> [nil, nil]

Argument exceeds the array size:

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.

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:

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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