I am just learning ruby and this seems to be an easy mistake I am doing here right?
def palindromic(str)
str.to_s
if str.reverse == str
puts "it is a palindromic number!"
end
end
palindromic(500)
Instead I am getting an error
Project4.rb:5:in `palindromic': undefined method `reverse' for 500:Fixnum (NoMet
hodError)
from Project4.rb:10:in `<main>'
You need to change the line str.to_s to str=str.to_s. One example to show you why so is below :
num = 12
num.to_s # => "12"
num # => 12
num=num.to_s
num # => "12"
Basically String#to_s change the receiver instance to the instance of String.But if the receiver is already the String instance,in that case receiver itself will be returned.
ar = [1,2]
ar.object_id # => 77603090
ar.to_s.object_id # => 77602480
str = 'Hello'
str.object_id # => 77601890
str.to_s.object_id # => 77601890
Related
I'm following this tutorial to learn about creating shapes and colors on a canvas. Here is the issue I'm running into: When I try to run the command in the run_command method and I take the first letter of my command (command[0]), it is returning the number 98 to me. I am trying to match the first letter of the command to a letter of the alphabet, but am unable to do so. What's strange though, is that when I remove the first letter with "command.delete "b"", the letter is removed and I'm free to use the rest of the string as I please.
Here is my code:
require 'ruby-processing'
class ProcessArtist < Processing::App
def setup
background(0, 0, 0)
end
def draw
# Do Stuff
end
def key_pressed
if #queue.nil?
#queue = ""
end
if key != "\n"
#queue = #queue + key
else
warn "Time to run the command: #{#queue}"
run_command(#queue)
#queue = ""
end
end
def run_command(command)
puts "Running command: #{command}"
puts command[0]
if command[0] == "b"
command.delete "b"
command.split(",")
background(command[0].to_i,command[1].to_i,command[2].to_i)
else
puts command[0]
command.delete "b"
command.split(",")
background(command[0].to_i,command[1].to_i,command[2].to_i)
end
end
end
ProcessArtist.new(:width => 800, :height => 800,
:title => "ProcessArtist", :full_screen => false)
Ah, I see what I did wrong. It should have been:
def run_command(command)
puts "Running command: #{command}"
puts command[0]
if command[0] = "b"
command.delete "b"
command.split(",")
background(command[0].to_i,command[1].to_i,command[2].to_i)
else
puts command[0]
command.delete "b"
command.split(",")
background(command[0].to_i,command[1].to_i,command[2].to_i)
end
end
It seems like you're using ruby version older than 1.9.
In old version of ruby (1.8-), String#\[\] return Fixnum object representing ASCII value, not String object.
>> RUBY_VERSION
=> "1.8.7"
>> 'bcd'[0]
=> 98
To get string back, use one of followings:
>> 'bcd'[0,1]
=> "b"
>> 'bcd'[0..0]
=> "b"
>> 'bcd'[0].chr # this will not work in Ruby 1.9+, so not recommended.
=> "b"
For comparison:
>> 'bcd'[0] == 'b'
=> false
>> 'bcd'[0] == ?b
=> true
>> 'bcd'.start_with? 'b'
=> true
I have the following string and want to define a method to append the letter 'd' to the end of it. One way I can do this is with the class << str idiom.
str = 'abc'
class << str
def frob
return self + "d"
end
end
Is there a way I can do this with the following syntax?
def str.frob
return str + 'd'
end
When I try to do this I get the undefined local variable or method 'str' for "abc":String (NameError)
str = 'abc'
def str.frob
p self
return self + 'd'
end
p str.frob
# >> "abc"
# >> "abcd"
str.singleton_methods # => [:frob]
str.object_id # => 79771730
You got the error because singleton_method #frob has its own local scope,where str is not legal. Thus you got the legitimate error. That method is created on the object "abc" having object_id,79771730.
>> a = 5
=> 5
>> b = a
=> 5
>> b = 4
=> 4
>> a
=> 5
how can I set 'b' to actually be 'a' so that in the example, the variable a will become four as well. thanks.
class Ref
def initialize val
#val = val
end
attr_accessor :val
def to_s
#val.to_s
end
end
a = Ref.new(4)
b = a
puts a #=> 4
puts b #=> 4
a.val = 5
puts a #=> 5
puts b #=> 5
When you do b = a, b points to the same object as a (they have the same object_id).
When you do a = some_other_thing, a will point to another object, while b remains unchanged.
For Fixnum, nil, true and false, you cannot change the value without changing the object_id. However, you can change other objects (strings, arrays, hashes, etc.) without changing object_id, since you don't use the assignment (=).
Example with strings:
a = 'abcd'
b = a
puts a #=> abcd
puts b #=> abcd
a.upcase! # changing a
puts a #=> ABCD
puts b #=> ABCD
a = a.downcase # assigning a
puts a #=> abcd
puts b #=> ABCD
Example with arrays:
a = [1]
b = a
p a #=> [1]
p b #=> [1]
a << 2 # changing a
p a #=> [1, 2]
p b #=> [1, 2]
a += [3] # assigning a
p a #=> [1, 2, 3]
p b #=> [1, 2]
You can't. Variables hold references to values, not references to other variables.
Here's what your example code is doing:
a = 5 # Assign the value 5 to the variable named "a".
b = a # Assign the value in the variable "a" (5) to the variable "b".
b = 4 # Assign the value 4 to the variable named "b".
a # Retrieve the value stored in the variable named "a" (5).
See this article for a more in-depth discussion of the topic: pass by reference or pass by value.
As has been noted the syntax you are using can not be done. Just throwing this out there though you could make a wrapper class it depends what you actually want to do
ruby-1.8.7-p334 :007 > class Wrapper
ruby-1.8.7-p334 :008?> attr_accessor :number
ruby-1.8.7-p334 :009?> def initialize(number)
ruby-1.8.7-p334 :010?> #number = number
ruby-1.8.7-p334 :011?> end
ruby-1.8.7-p334 :012?> end
=> nil
ruby-1.8.7-p334 :013 > a = Wrapper.new(4)
=> #<Wrapper:0x100336db8 #number=4>
ruby-1.8.7-p334 :014 > b = a
=> #<Wrapper:0x100336db8 #number=4>
ruby-1.8.7-p334 :015 > a.number = 6
=> 6
ruby-1.8.7-p334 :016 > a
=> #<Wrapper:0x100336db8 #number=6>
ruby-1.8.7-p334 :017 > b
=> #<Wrapper:0x100336db8 #number=6>
You can use arrays:
a = [5]
b = a
b[0] = 4
puts a[0] #=> 4
This idea is based on this answer.
Just for the sake of reference.
>> a = 5
=> 5
>> a.object_id
=> 11
>> b = a
=> 5
>> b.object_id
=> 11
>> b = 4
=> 4
>> b.object_id
=> 9
>> a.object_id
=> 11
# We did change the Fixnum b Object.
>> Fixnum.superclass
=> Integer
>> Integer.superclass
=> Numeric
>> Numeric.superclass
=> Object
>> Object.superclass
=> BasicObject
>> BasicObject.superclass
=> nil
I hope this gives us all a little better understanding about objects in Ruby.
One option in cases where you feel you would like to have direct pointer operations is to use the replace method of Hashes, Arrays & Strings.
this is useful for when you would like to have a method return a variable that a proc the method sets up will change at a later date, and don't want the annoyance of using a wrapper object.
example:
def hash_that_will_change_later
params = {}
some_resource.on_change do
params.replace {i: 'got changed'}
end
params
end
a = hash_that_will_change_later
=> {}
some_resource.trigger_change!
a
{i: 'got changed'}
It's probably better generally to use explicit object wrappers for such cases, but this pattern is useful for building specs/tests of asynchronous stuff.
I'm no Ruby expert. But for a technically crazy kluge...that would only work if you felt like going through eval every time you worked with a variable:
>> a = 5
=> 5
>> b = :a
=> :a
>> eval "#{b} = 4"
=> 4
>> eval "#{a}"
=> 4
>> eval "#{b}"
=> 4
Note that a direct usage of b will still give you :a and you can't use it in expressions that aren't in eval:
>> b
=> :a
>> b + 1
NoMethodError: undefined method `+' for :a:Symbol
...and there are certainly a ton of caveats. Such as that you'd have to capture the binding and pass it around in more complex scenarios...
'pass parameter by reference' in Ruby?
#Paul.s has an answer for if you can change the point of declaration to be a wrapper object, but if you can only control the point of reference then here's a BasicReference class I tried:
class BasicReference
def initialize(r,b)
#r = r
#b = b
#val = eval "#{#r}", #b
end
def val=(rhs)
#val = eval "#{#r} = #{rhs}", #b
end
def val
#val
end
end
a = 5
puts "Before basic reference"
puts " the value of a is #{a}"
b = BasicReference.new(:a, binding)
b.val = 4
puts "After b.val = 4"
puts " the value of a is #{a}"
puts " the value of b.val is #{b.val}"
This outputs:
Before basic reference
the value of a is 5
After b.val = 4
the value of a is 4
the value of b.val is 4
Is there a built-in method in Ruby to support this?
if you are in Rails, you can convert 1 to 1st, 2 to 2nd, and so on, using ordinalize.
Example:
1.ordinalize # => "1st"
2.ordinalize # => "2nd"
3.ordinalize # => "3rd"
...
9.ordinalize # => "9th"
...
1000.ordinalize # => "1000th"
And if you want commas in large numbers:
number_with_delimiter(1000, :delimiter => ',') + 1000.ordinal # => "1,000th"
in ruby you do not have this method but you can add your own in Integer class like this.
class Integer
def ordinalize
case self%10
when 1
return "#{self}st"
when 2
return "#{self}nd"
when 3
return "#{self}rd"
else
return "#{self}th"
end
end
end
22.ordinalize #=> "22nd"
How about Linguistics? Its not built in though. If you want built in , you have to set it up using hashes etc..
See here also for examples
I wanted an ordinalize method that has "first, second, third" rather than '1st, 2nd, 3rd' - so here's a little snippet that works up to 10 (and falls back to the Rails ordinalize if it can't find it).
class TextOrdinalize
def initialize(value)
#value = value
end
def text_ordinalize
ordinalize_mapping[#value] || #value.ordinalize
end
private
def ordinalize_mapping
[nil, "first", "second", "third", "fourth", "fifth", "sixth", "seventh",
"eighth", "ninth", "tenth" ]
end
end
Here's how it works:
TextOrdinalize.new(1).text_ordinalize #=> 'first'
TextOrdinalize.new(2).text_ordinalize #=> 'second'
TextOrdinalize.new(0).text_ordinalize #=> '0st'
TextOrdinalize.new(100).text_ordinalize #=> '100th'
if you are not in Rails you could do
def ordinalize(n)
return "#{n}th" if (11..13).include?(n % 100)
case n%10
when 1; "#{n}st"
when 2; "#{n}nd"
when 3; "#{n}rd"
else "#{n}th"
end
end
ordinalize 1
=> "1st"
ordinalize 2
=> "2nd"
ordinalize 11
=> "11th"
Using humanize gem, is probably the easiest way. But, yes, it is not built in, however it has only one dependency, so I think its a pretty good choice..
require 'humanize'
2.humanize => "two"
Why isnt that working:
>> s = "hi"
=> "hi"
>> s == ("hi"|"ho")
NoMethodError: undefined method `|' for "hi":String
from (irb):2
>>
I don't get it.. Is there a solution for this kind of syntax? Because
s == ("hi"|"ho")
#is shorther than
s == "hi" || s == "ho"
Yes, the bitwise operator | is not defined in the String class: http://ruby-doc.org/core/classes/String.html
Consider this for expressiveness:
["hi", "ho"].include? myStr
irb(main):001:0> s = "hi"
=> "hi"
irb(main):002:0> ["hi", "ho"]
=> ["hi", "ho"]
irb(main):003:0> ["hi", "ho"].include? s
=> true
irb(main):004:0> s = "foo"
=> "foo"
irb(main):005:0> ["hi", "ho"].include? s
=> false
In most high level languages that syntax will not work, you have to stick to the longer syntax of:
s == "hi" || s == "ho"
Note that | is a bitwise or, whereas || is a regular or
You could use the include? method on array if you've got several == tests to do:
["hi", "ho"].include?(s)
Not shorter for two checks admittedly but it will be shorter for three or more.
This syntax doesn't exist in any language as far as I know.
What you are saying
s == ("hi"|"ho")
Literally translates to 'bitwise OR the strings "hi" and "ho" together and then compare them with s'. If you can't see why this is not what you are looking for, try writing down the ASCII codes for "hi" and "ho" and then bitwise ORing them together. You are going to get complete gibberish.
You could make it work that way:
irb> class Pair
def initialize(strA,strB)
#strA,#strB = strA,strB
end
def ==(string)
string == #strA || string == #strB
end
def |(other)
Pair.new(self,other)
end
end
#=> nil
irb> class String
def |(other)
Pair.new(self,other)
end
alias old_equals :==
def ==(other)
if other.kind_of? Pair
other == self
else
old_equals other
end
end
end
#=> nil
irb> ("one"|"two") == "one"
#=> true
irb> ("one"|"two") == "two"
#=> true
irb> ("one"|"two") == "three"
#=> false
irb> "one" == ("one"|"two")
#=> true
irb> "three" == ("one"|"two"|"three")
#=> true
But since this involves some monkey-patching of a fairly lowlevel class, I wouldn't advise relying on it. Other people will hate reading your code.
Ruby supports binary 'or' and other binary operations on values of type Fixnum and Bignum, meaning any integer. Bitwise operations aren't supported on strings or any other type, as far as I know.
As other people have mentioned, you probably want something other than binary operations altogether. However, you can easily get integer representations of characters, so you can compare characters like so:
a = "Cake"
b = "Pie"
puts a[0] | b[0] # Prints "83" - C is 67 and P is 80.
You can get an array of the comparisons easily with some conversions.
a = "Cake"
b = "Pie " # Strings of uneven length is trivial but more cluttered.
a_arr = a.split(//)
b_arr = b.split(//)
c_arr = []
a.each_with_index { |char, i| c.push(a[i].to_i | b[i].to_i) }
# If you *really* want an ASCII string back...
c = c_arr.collect(&:chr).join
You could use a regex:
Like so:
regex = /hi|ho/
s = "hi"
t = "foo"
s =~ regex
#=> 0
t =~ regex
#=> nil