# String concatenation in ruby

**URL:** <https://www.ruby-forum.com/t/string-concatenation-in-ruby/192787>\
**Category:** Ruby\
**Created:** [August 5, 2010, 3:47pm UTC](https://www.ruby-forum.com/t/string-concatenation-in-ruby/192787 "2010-08-05T15:47:03Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![yani\_engico](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/y/919ad9/32.png) [@yani\_engico](https://www.ruby-forum.com/u/yani_engico)\
**Post date:** [August 5, 2010, 3:47pm UTC](https://www.ruby-forum.com/t/string-concatenation-in-ruby/192787/1 "2010-08-05T15:47:03Z")

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Hi,

This seems to be a basic question but i would like to know why.

String concatenation in rails can be done in the following three ways:

1. a+b+c
2. a\<\<b\<\<c
3. “#{a}#{b}#{c}”

where a b c are three variables

Which is the good way to go about concatenation and why?

a+b+c is not good because it creates temp string objects i guess

But i would really like to know of the three which is better and why. Is  
there any performance difference in using them

Thanks in advance

---

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**Author:** ![yani\_engico](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/y/919ad9/32.png) [@yani\_engico](https://www.ruby-forum.com/u/yani_engico)\
**Post date:** [August 5, 2010, 4:58pm UTC](https://www.ruby-forum.com/t/string-concatenation-in-ruby/192787/2 "2010-08-05T16:58:05Z")

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On 08/05/2010 06:47 AM, Prachi T. wrote:

> where a b c are three variables
> 
> Which is the good way to go about concatenation and why?
> 
> a+b+c is not good because it creates temp string objects i guess
> 
> But i would really like to know of the three which is better and why. Is  
> there any performance difference in using them
> 
> Thanks in advance

As you mention, using + will create strings which then need to be  
garbage collected. Using \<\< will modify the left-most variable, which  
you may not always desire. The other downside to using + or \<\< is that  
they will raise an error if any of your variables are not strings. If  
you use interpolation, to\_s will be called on the variables which may  
save your program from crashing.

Interpolation also appears to be the fastest method:  
[http://rubybenchmark.com/reports/6](http://rubybenchmark.com/reports/6)

-Justin

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<div class="post-metadata">

**Author:** ![yani\_engico](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/y/919ad9/32.png) [@yani\_engico](https://www.ruby-forum.com/u/yani_engico)\
**Post date:** [August 5, 2010, 4:58pm UTC](https://www.ruby-forum.com/t/string-concatenation-in-ruby/192787/3 "2010-08-05T16:58:41Z")

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On Thu, Aug 5, 2010 at 2:47 PM, Prachi T.  
[removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)wrote:

> there any performance difference in using them  
> Thanks in advance

You can experiment using benchmark (see below) or hitimes (which I  
haven’t  
tried yet), and there may well be others. I think the results should be  
taken more as indications rather than definitive, but you can see from  
the  
following that whether one way is faster than another can depend on the  
data. (I hope that the formatting of the times is ok - it looks  
diabolical  
in this draft.)

require “benchmark”  
r1 = r2 = r3 = nil

a = nil  
av = “Karel Capek”.freeze  
b = " wrote"  
c = " War with the Newts"  
kt = 100\_000  
Benchmark.bmbm do |r|  
r.report(“a+b+c” ) {kt.times { a = av.dup; r1 = a + b + c } }  
r.report(“a\<\<b\<\<c” ) {kt.times { a = av.dup; r2 = a \<\< b \<\< c } }  
r.report(‘#{a}#{b}#{c}’) {kt.times { a = av.dup; r3 = “#{a}#{b}#{c}” } }  
end  
p r1, r2, r3

av = (“kc " \* 100).freeze  
b = " wr” \* 50  
c = " WN" \* 50  
kt = 100\_000  
Benchmark.bmbm do |r|  
r.report(“a+b+c” ) {kt.times { a = av.dup; r1 = a + b + c } }  
r.report(“a\<\<b\<\<c” ) {kt.times { a = av.dup; r2 = a \<\< b \<\< c } }  
r.report(‘#{a}#{b}#{c}’) {kt.times { a = av.dup; r3 = “#{a}#{b}#{c}” } }  
end

##########=\>  
run: “C:\ruby19\bin\ruby.exe” -v “aaa-bm-str.rb”  
ruby 1.9.1p243 (2009-07-16 revision 24175) [i386-mingw32]

Rehearsal ------------------------------------------------  
a+b+c 0.405000 0.000000 0.405000 ( 0.470000)  
a\<\<b\<\<c 0.406000 0.000000 0.406000 ( 0.410000)  
#{a}#{b}#{c} 0.468000 0.000000 0.468000 ( 0.515000)  
--------------------------------------- total: 1.279000sec  
user system total real  
a+b+c 0.452000 0.000000 0.452000 ( 0.465000)  
a\<\<b\<\<c 0.390000 0.000000 0.390000 ( 0.395000)  
#{a}#{b}#{c} 0.499000 0.000000 0.499000 ( 0.520000)  
“Karel Capek wrote War with the Newts”  
“Karel Capek wrote War with the Newts”  
“Karel Capek wrote War with the Newts”

Rehearsal ------------------------------------------------  
a+b+c 0.624000 0.016000 0.640000 ( 0.690000)  
a\<\<b\<\<c 0.499000 0.000000 0.499000 ( 0.515000)  
#{a}#{b}#{c} 0.671000 0.000000 0.671000 ( 0.650000)  
--------------------------------------- total: 1.810000sec  
user system total real  
a+b+c 0.639000 0.000000 0.639000 ( 0.645000)  
a\<\<b\<\<c 0.515000 0.031000 0.546000 ( 0.540000)  
#{a}#{b}#{c} 0.624000 0.000000 0.624000 ( 0.680000)