method

shift

v1_9_3_392 - Show latest stable - Class: Array

shift(*args)

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"]

static VALUE
rb_ary_shift_m(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_take_first_or_last(argc, argv, ary, ARY_TAKE_FIRST);
    n = RARRAY_LEN(result);
    if (ARY_SHARED_P(ary)) {
        if (ARY_SHARED_NUM(ARY_SHARED(ary)) == 1) {
            rb_mem_clear(RARRAY_PTR(ary), n);
        }
        ARY_INCREASE_PTR(ary, n);
    }
    else {
        MEMMOVE(RARRAY_PTR(ary), RARRAY_PTR(ary)+n, VALUE, RARRAY_LEN(ary)-n);
    }
    ARY_INCREASE_LEN(ary, -n);

    return result;
}

1Note

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

nhance · Apr 1, 20103 thanks

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

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

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

shift

1Note

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

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