Hi,
I wonder what is the difference between s=s+â?aâ? ans s<< â?aâ??
Somebody told me that s<< â?aâ? concatenates the string without mutation.
Is that right?
Thanks,
Alan
On Jun 21, 2006, at 3:15 PM, Alan M. wrote:
–
Posted via http://www.ruby-forum.com/.
Someone told you wrong.
s = s + “a” is concatenate s and “a” and return a new string, bind it
to the variable a.
s << “a” is append “a” to the string referenced by the variable s. It
changes s in place.
Of course, this is exactly the kind of question to be answered by ri.
ri String#<<
ri String#+
On 6/21/06, Alan M. [email protected] wrote:
Hi,
I wonder what is the difference between s=s+“a” ans s<< “a”?
s = s + “a”
(1) compute a new String object “s” + a
(2) set s as a reference to the newly created object
s<<“a”
(1) append “a” to the String object s refers to.
The latter is much faster and should be prefered when possible (it will
not
be possible if s is frozen e.g.)
Cheers
Robert
Somebody told me that s<< “a” concatenates the string without mutation.
Is that right?
Thanks,
Alan–
Posted via http://www.ruby-forum.com/.
–
Deux choses sont infinies : l’univers et la bêtise humaine ; en ce qui
concerne l’univers, je n’en ai pas acquis la certitude absolue.
- Albert Einstein
2006/6/21, Simon Kröger [email protected]:
I think
s = s + “a” #
or
s += “a”should be the norm as long as you do not know that using it will cause
you problems (really only performance problems come to my mind)
I use the rule exactly the other way round: usually use << unless that
might cause problems. There’s a lot of code out there that does +=
while all it wants to do is appending. += is less efficient and with
my C++ background << more looks like “append”.
end
hello = ‘hello’
greet_matz hello
greet_nobu hello#=> hello matz!
#=> hello matz! nobu!you will get what you expect if you use +=
It depends on what you expect. If methods are expected to get
something that they append stuff to then the observed behavior is
exactly what you expect and want. 
For example, if you write a method that should append info about the
current instance to something then you should use << because then even
an IO object can be passed and the code still works as expected.
As generally, you should know your tools and be knowing what you do.
Kind regards
robert
On 6/21/06, Simon Kröger [email protected] wrote:
(1) compute a new String object “s” + a
I think
s = s + “a” #
or
s += “a”should be the norm as long as you do not know that using it will cause
you problems (really only performance problems come to my mind)
s << “a”
is just what you should do instead
of
s = s+ “a”
unless of course you get paid for GC 
Have a look at this:
def greet_matz greeting
greeting << ’ matz!’
puts greeting
end
Calling writer methods on parameters is asking for side effects, that
might
be good or bad, I do not want to discuss that right now, but has
nothing
to do with the question of the OP.
def greet_nobu greeting
you will get what you expect if you use +=
Forgive me for being blunt: I will get what I expect if I use <<, I
might
not get what you expected.
cheers
Simon
Fortunately I did not state my favorite way to use puts
puts some_variable * 1 << “some text” << …
Cheers
Robert
–
Deux choses sont infinies : l’univers et la bêtise humaine ; en ce qui
concerne l’univers, je n’en ai pas acquis la certitude absolue.
- Albert Einstein
Robert D. wrote:
s<<“a”
(1) append “a” to the String object s refers to.
The latter is much faster and should be prefered when possible (it will not
be possible if s is frozen e.g.)
I think
s = s + “a” #
or
s += “a”
should be the norm as long as you do not know that using it will cause
you problems (really only performance problems come to my mind)
Have a look at this:
def greet_matz greeting
greeting << ’ matz!’
puts greeting
end
def greet_nobu greeting
greeting << ’ nobu!’
puts greeting
end
hello = ‘hello’
greet_matz hello
greet_nobu hello
#=> hello matz!
#=> hello matz! nobu!
you will get what you expect if you use +=
cheers
Simon
Most readable + safe for me is e.g.:
puts “Hello, #{name}!”
puts “your calculation: #{arg1} * #{arg2} = #{arg1 * arg2}”
Robert D. schrieb:
will cause
you problems (really only performance problems come to my mind)
I use the rule exactly the other way round: usually use << unless that
might cause problems. There’s a lot of code out there that does +=
while all it wants to do is appending. += is less efficient and with
my C++ background << more looks like “append”.
Well, if you realy know what you do and if ‘that might cause problems’
there is of course no problem with <<. ‘+= is less efficient’ smells
like
premature optimization.
you will get what you expect if you use +=
It depends on what you expect. If methods are expected to get
something that they append stuff to then the observed behavior is
exactly what you expect and want.
Hmm, I (but that may be just me) wouldn’t write a method that ‘get
something that they append stuff to’. I would write a method which will
return the stuff and let the caller append it to whatever he wishes.
(I like it a bit functional style and do not like side effects)
For example, if you write a method that should append info about the
current instance to something then you should use << because then even
an IO object can be passed and the code still works as expected.
Yes, if I would write such a method, yes. If appending is exactly the
operation I want, I use it. sure.
As generally, you should know your tools and be knowing what
you do.
That sums it up quite perfect.
Kind regards
robert
cheers
Simon
From: Pete [mailto:[email protected]]
Sent: Wednesday, June 21, 2006 11:45 PMMost readable + safe for me is e.g.:
puts “Hello, #{name}!”
puts “your calculation: #{arg1} * #{arg2} = #{arg1 * arg2}”
In case this wasn’t obvious: this was an example.
As there is no syntactical difference between pass by value
and pass by reference in ruby I try to avoid modifying
parameters and would use += in favour of <<. (at least in such
cases)
cheers
Simon
p.s.: oh well, I know there is no such thing as pass by value
in ruby at all, it just feels like it for immediate values.
From: Robert D. [mailto:[email protected]]
Sent: Wednesday, June 21, 2006 11:10 PM
s << “a”
is just what you should do instead
of
s = s+ “a”
unless of course you get paid for GC
I think that should be solved in the interpreter not by the
programmer. Meanwhile you are right, of course << is more
efficient.
Calling writer methods on parameters is asking for side
effects, that might
I guess that was my whole point.
be good or bad, I do not want to discuss that right now, but
has nothing
to do with the question of the OP.
That might be true.
Fortunately I did not state my favorite way to use puts
puts some_variable * 1 << “some text” << …
cheers
Simon