instance method

Hash#shift

() -> [ K, V ]?

shift → [key, value] or nil

static VALUE
rb_hash_shift(VALUE hash)
{
    struct shift_var var;

    rb_hash_modify_check(hash);
    if (RHASH_AR_TABLE_P(hash)) {
        var.key = Qundef;
        if (!hash_iterating_p(hash)) {
            if (ar_shift(hash, &var.key, &var.val)) {
                return rb_assoc_new(var.key, var.val);
            }
        }
        else {
            rb_hash_foreach(hash, shift_i_safe, (VALUE)&var);
            if (!UNDEF_P(var.key)) {
                rb_hash_delete_entry(hash, var.key);
                return rb_assoc_new(var.key, var.val);
            }
        }
    }
    if (RHASH_ST_TABLE_P(hash)) {
        var.key = Qundef;
        if (!hash_iterating_p(hash)) {
            if (st_shift(RHASH_ST_TABLE(hash), &var.key, &var.val)) {
                return rb_assoc_new(var.key, var.val);
            }
        }
        else {
            rb_hash_foreach(hash, shift_i_safe, (VALUE)&var);
            if (!UNDEF_P(var.key)) {
                rb_hash_delete_entry(hash, var.key);
                return rb_assoc_new(var.key, var.val);
            }
        }
    }
    return Qnil;
}

Removes and returns the first entry of self as a 2-element array; see Entry Order:

Example

h = {foo: 0, bar: 1, baz: 2}
h.shift # => [:foo, 0]
h       # => {bar: 1, baz: 2}

Returns nil if self is empty.

Related: see Methods for Deleting.

Ruby version changes

3.2
- Hash#shift now always returns nil if the hash is empty, instead of returning the default value or calling the default proc. [Bug #16908]

See also #select! #size #select #slice also in 4.1 · 3.4 · 3.3 · 3.2 · 3.1 · 3.0

‹ prev#select! next ›#size