Ruby Newbie homepage Ruby Newbie homepage

How to use

Quick guide

Official content
Sets self to consider only identity in comparing keys; two keys are considered the same only if they are the same object; returns self.
By default, these two object are considered to be the same key, so s1 will overwrite s0:
s0 = 'x'
s1 = 'x'
h = {}
h.compare_by_identity? # => false
h[s0] = 0
h[s1] = 1
h # => {"x"=>1}
After calling #compare_by_identity, the keys are considered to be different, and therefore do not overwrite each other:
h = {}
h.compare_by_identity # => {}
h.compare_by_identity? # => true
h[s0] = 0
h[s1] = 1
h # => {"x"=>0, "x"=>1}
rb_hash_compare_by_id(VALUE hash)
    VALUE tmp;
    st_table *identtable;

    if (rb_hash_compare_by_id_p(hash)) return hash;

    ar_force_convert_table(hash, __FILE__, __LINE__);

    tmp = hash_alloc(0);
    identtable = rb_init_identtable_with_size(RHASH_SIZE(hash));
    RHASH_ST_TABLE_SET(tmp, identtable);
    rb_hash_foreach(hash, rb_hash_rehash_i, (VALUE)tmp);
    RHASH_ST_TABLE_SET(hash, identtable);

    return hash;

Was this page useful?