Ruby

This patch will add pre-allocation in string interpolation.
By this, unnecessary capacity resizing is avoided.

For small strings, optimized rb_str_resurrect operation is faster, so pre-allocation is done only when concatenated strings are large.
MIN_PRE_ALLOC_SIZE was decided by experimenting with local machine (x86_64-apple-darwin 16.5.0, Apple LLVM version 8.1.0 (clang - 802.0.42)).

String interpolation will be faster around 72% when large string is created.

Before

Calculating ------------------------------------- Large string interpolation 1.276M (± 5.9%) i/s - 6.358M in 5.002022s Small string interpolation 5.156M (± 5.5%) i/s - 25.728M in 5.005731s 

After

Calculating ------------------------------------- Large string interpolation 2.201M (± 5.8%) i/s - 11.063M in 5.043724s Small string interpolation 5.192M (± 5.7%) i/s - 25.971M in 5.020516s 

Test code

require 'benchmark/ips' Benchmark.ips do |x| x.report "Large string interpolation" do |t| a = "Hellooooooooooooooooooooooooooooooooooooooooooooooooooo" b = "Wooooooooooooooooooooooooooooooooooooooooooooooooooorld" t.times do "#{a}, #{b}!" end end x.report "Small string interpolation" do |t| a = "Hello" b = "World" t.times do "#{a}, #{b}!" end end end 

Patch
https://github.com/ruby/ruby/pull/1626