method

shift

v1_8_7_72 - Show latest stable - 1 note - Class: Array

shift(...) public

Returns the first element of self and removes it (shifting all other elements down by one). Returns nil if the array is empty.

If a number n is given, returns an array of the first n elements (or less) just like array.slice!(0, n) does.

   args = [ "-m", "-q", "filename" ]
   args.shift     #=> "-m"
   args           #=> ["-q", "filename"]

   args = [ "-m", "-q", "filename" ]
   args.shift(2)  #=> ["-m", "-q"]
   args           #=> ["filename"]

Show source

/*
 *  call-seq:
 *     array.shift    -> obj or nil
 *     array.shift(n) -> array
 *  
 *  Returns the first element of <i>self</i> and removes it (shifting all
 *  other elements down by one). Returns <code>nil</code> if the array
 *  is empty.
 *
 *  If a number _n_ is given, returns an array of the first n elements
 *  (or less) just like <code>array.slice!(0, n)</code> does.
 *     
 *     args = [ "-m", "-q", "filename" ]
 *     args.shift     #=> "-m"
 *     args           #=> ["-q", "filename"]
 *
 *     args = [ "-m", "-q", "filename" ]
 *     args.shift(2)  #=> ["-m", "-q"]
 *     args           #=> ["filename"]
 */

static VALUE
rb_ary_shift_m(argc, argv, ary)
    int argc;
    VALUE *argv;
    VALUE ary;
{
    VALUE result;
    long n;

    if (argc == 0) {
        return rb_ary_shift(ary);
    }

    rb_ary_modify_check(ary);
    result = ary_shared_first(argc, argv, ary, Qfalse);
    n = RARRAY(result)->len;
    if (FL_TEST(ary, ELTS_SHARED)) {
        RARRAY(ary)->ptr += n;
        RARRAY(ary)->len -= n;
        }
    else {
        MEMMOVE(RARRAY(ary)->ptr, RARRAY(ary)->ptr+n, VALUE, RARRAY(ary)->len-n);
        RARRAY(ary)->len -= n;
    }

    return result;
}

April 1, 2010

3 thanks

Doesn't return nil on empty array when param is given

This does not return nil if the array is empty and n is given.

[].shift(2) # => []

a = []
a.shift(2) # => []
a # => []

shift

Related methods

Doesn't return nil on empty array when param is given