Bug #9079

Interpolated Symbol creates unnecessary intermediate String on the heap

Added by wycats (Yehuda Katz) over 4 years ago. Updated over 2 years ago.

Target version:
ruby -v:
ruby 2.0.0p343 (2013-10-31) [x86_64-linux]


This case:

x = "world"
y = :"hello#{world}!"

allocates one T_STRING according to ObjectSpace.count_objects. Since all of the concatenation happens as part of the symbol generation, it shouldn't be necessary to create a Ruby string.


#1 [ruby-core:58161] Updated by charliesome (Charlie Somerville) over 4 years ago

To shed a bit of light on why this happens, it turns out :"" syntax is just sugar for "".intern:

~ trunk λ ruby --dump=insns -e ':"hello #{123}"'
== disasm: <RubyVM::InstructionSequence:<main>@-e>======================
0000 trace            1                                               (   1)
0002 putobject        "hello "
0004 putobject        123
0006 tostring
0007 concatstrings    2
0009 opt_send_simple  <callinfo!mid:intern, argc:0, ARGS_SKIP>
0011 leave

#2 [ruby-core:59044] Updated by ko1 (Koichi Sasada) over 4 years ago

  • Target version set to 2.6

Does it has huge impact?
It is easy to add an instruction (replace concatstrings to concatstrings_and_make_it_symbol) or add a method like that.
However, it has a bit problem about encoding.
Current implementation is easy and safe, because we can catch up encoding related change to String.
I want to remain this issue, if this does not have huge impact for performance.

#3 Updated by ko1 (Koichi Sasada) over 2 years ago

  • Status changed from Open to Feedback

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