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Allow Array#join to allocate smaller strings

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rb_str_buf_new always allocates at least 127 bytes of capacity, even
when less is requested.

    > ObjectSpace.dump(%w[a b c].join)
    {"address":"0x7f935f06ebf0", "type":"STRING", "class":"0x7f935d8b7bb0", "bytesize":3, "capacity":127, "value":"abc", "encoding":"UTF-8", "memsize":168, "flags":{"wb_protected":true}}

Instead, by using rb_str_new and then setting the length to 0, we can
allocate the exact amount of memory needed, without extra capacity.

    > ObjectSpace.dump(%w[a b c].join)
    {"address":"0x7f903fcab530", "type":"STRING", "class":"0x7f903f8b7988", "embedded":true, "bytesize":3, "value":"abc", "encoding":"UTF-8", "memsize":40, "flags":{"wb_protected":true}}
This commit is contained in:
John Hawthorn 2019-06-26 09:52:30 -07:00 committed by Aaron Patterson
parent b1678338e5
commit 9d298b9dab
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1 changed files with 3 additions and 1 deletions
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array.c
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@ -2368,7 +2368,9 @@ rb_ary_join(VALUE ary, VALUE sep)
len += RSTRING_LEN(tmp);
}
result = rb_str_buf_new(len);
result = rb_str_new(0, len);
rb_str_set_len(result, 0);
if (taint) OBJ_TAINT(result);
ary_join_0(ary, sep, RARRAY_LEN(ary), result);