Jaiden Mispy
First time I've hit the string concatenation issue in Ruby. This wastes ~1g of memory for a 600k character input:pic.twitter.com/8v1tz9Tdtr
Charlie Somerville
@m1sp fun fact: this isn't an issue in CPython because it can cheat and do an in-place append if the left hand side's ref count is 1
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@charliesome@m1sp uhhhh even if it didn't, you should only have two copies of each string live at any given time, htf does that get to 1g -
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@charliesome@m1sp whoops well then this isn't an issue in CPython because it's mostly refcounted 8) -
@charliesome@m1sp but string building by concatenation is O(nm) so you shouldn't be doing it anyway tsk tsk -
Array#join is faster than either form of concatenation, as
@eevee points outhttp://stackoverflow.com/a/23555375/1983739 … -
@m1sp that's a bad benchmark, the Array#join case is only faster because it runs less Ruby code and allocates fewer objects -
@m1sp Array#join uses a loop and String#<< internally (although it calls the C function for #<< directly rather than making a method call)
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@AndreaFaulds@charliesome and there is no such branching to be found in the Ruby equivalent, yep ^^ https://github.com/ruby/ruby/blob/trunk/string.c#L1444 … - Show more
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@m1sp@charliesome In CPython not all strings are expandable that way. In practice it's a chancy optimization and you shouldn't count on it. -
@charliesome@m1sp A 2005 view of the CPython 2.4 situation is http://utcc.utoronto.ca/~cks/space/blog/python/ExaminingStringConcatOpt … . I'm sure there's been changes since for eg Unicode.
Chris Siebenmann
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