Bug #9079: Interpolated Symbol creates unnecessary intermediate String on the heap

• Status: Closed
• Assignee: ko1 (Koichi Sasada)
• Target version: -
• ruby -v: ruby 2.0.0p343 (2013-10-31) [x86_64-linux]

[wycats (Yehuda Katz)]

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.

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

[ko1 (Koichi Sasada)]

• 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.

[ko1 (Koichi Sasada)]

• Status changed from Open to Feedback

[jeremyevans0 (Jeremy Evans)]

• Status changed from Feedback to Closed
• Backport deleted (1.9.3: UNKNOWN, 2.0.0: UNKNOWN)