?. is a string literal:
?. #=> "."
However, I failed to declare a variable with a name like that:
?some_var = 100 #=> Error
How is?something invalid when ?. is valid?
? cannot describe any string literal; it is valid only for a single character.
Even if ?something were a valid string literal (counter to fact),
?something = ...
will be assignment to a string, which does not make sense. You cannot assign a value to a string.
?a is the same as "a". So it is a value, which belongs on the right hand side of an assignment, not the left hand side. It is not a variable name.
The Syntax exists as a relic from Ruby <=1.9, where it was equivalent to "a".bytes[0] and ?d could be used to shave off one character of code golf. I haven't seen any legitimate use otherwise.
Related
I have this line:msg = "Couldn't find column: #{missing_columns.map(&:inspect).join(',')}"
that outputs: Couldn't find column: /firstname/i, /lastname/i
Is there a way that I can use gsub to return only the name of the column without the "/" and "/i"? Or is there a better way to do it?
I've tried errors = msg.gsub(/\/|i/, '') but it returns the the first missing column with "frstname".
Given that these appear to be case insensitive regular expressions meaning
missing_columns
#=> [/firstname/i,/lastname/i]
In this case rather than converting them to strings and trying to manipulate them from there you can use methods that a Regexp already responds to e.g. Regexp#source
Regexp#source - "Returns the original string of the pattern." It will not return the literal boundaries (/) or the options (i in this case)
missing_columns.map(&:source).join(', ')
#=> "firstname, lastname"
/\/|i/
Let's break this down. The // on the outside are delimiters, sort of like quotation marks for strings. So the actual regex is on the inside.
\/|i
\/ says to match a literal forward slash. \ prevents it from being interpreted as the end of the regular expression.
i says to match a literal i. So far nothing fancy. But | is an alternation. It says to match either the thing on the left or the thing on the right. Effectively, this removes all slashes and i from your string. You want to remove all / or /i, but not i on its own. You can still do that with alternation, provided you include the slash on both sides.
/\/|\/i/
You can also do it more compactly with the ? modifier, which makes the thing before it optional.
/\/i?/
Finally, you can avoid the /\/ fencepost shenanigans by using the %r{...} regular expression form rather than /.
%r{/i?}
All in all, that's
errors = msg.gsub(%r{/i?}, '')
It seems that missing_columns contains an array of Regexps. So you can use Regexp#source instead of Regexp#inspect.
For instance
msg = "Couldn't find column: #{missing_columns.map(&:source).join(', ')}"
pp msg # => "Couldn't find column: firstname, lastname"
instead of
msg = "Couldn't find column: #{missing_columns.map(&:inspect).join(', ')}"
pp msg # => "Couldn't find column: /firstname/i, /lastname/i"
Feel free to browse the documentation for Regexp#source.
hope this helps!
The following code always outputs "not":
print "input a number please. "
TestNumber = gets
if TestNumber % 2 == 0
print "The number is even"
else
print "The number is not even"
end
What is going wrong with my code?
The gets() method returns an object of type String.
When you call %() on a String object, the return value is a new String object (usually it changes the text. You can read more about string formatting here).
Since there are no String objects that == 0, the if/else will always take the same path.
If you want to use the return value of gets() like a number, you will need to transform it into one first. The simplest approach is probably to use the to_i() method on String objects, which returns a new 'Integer' object. If you're doing something where the user input will not always be an integer (e.g. 3.14 or 1.5), you might need to use a different approach.
One last thing: in your example the result of gets() is saved into a constant called TestNumber. Constants are different to normal variables, and they will probably cause problems if you're not using them intentionally. Normal variables don't start with capital letters. (You can read more about ruby variables here). In ruby you need to write you variable names like this: test_number.
I suspect your Testnumber variable might be interpreted as a string during the operation. make sure the testnum is converted to an integer first even if you put in say 100 it could be its being interpreted as the stirng "100" and not the integer 100.
A similar issue can be found here: Ruby Modulo Division
You have to convert TestNumber from string to integer, as your input has linefeed and/or other unwanted characters that do not match an integer.
Use TestNumber = gets.to_i to convert to integer before testing.
I want to create a simple function in Ruby that will check if the given string contains any unicode characters in the ranges such as the following:
U+007B -- U+00BF
U+02B0 -- U+037F
U+2000 -- U+2BFF
How can I accomplish this? Google is coming up blank for me, all things about removing unicode characters or checking if a string contains unicode.
The easiest thing would probably be a regex using String#index, String#match, or even String#[]:
string.index(/[\u007B-\u00BF\u02B0-\u037F\u2000-\u2BFF]/)
string.match(/[\u007B-\u00BF\u02B0-\u037F\u2000-\u2BFF]/)
string[/[\u007B-\u00BF\u02B0-\u037F\u2000-\u2BFF]/]
All three will give you nil (which is falsey) if they don't find the pattern and non-nil (which will be truthy) if they do.
I would do as below:
my_string = "{ How are you ?}"
puts my_string.chars.any? { |chr| ("\u007B".."\u00BF").include?(chr) }
#=> true
I am trying to retrieve the value of a letter in an array. The array I have is:
a = ["a","b","c","d","e","f","g","h"].
If I want to retrieve a letter's value, the code is:
?a
However, when I tried ?a[5] it gives me 0. Does anyone know why this is the case?
--sorry to clarify I am using 1.8.7 :)
Actually, as of Ruby 1.9. ?a will give you the string "a", where it used to give you the ASCII code for that character. It's just another (limited) string literal mechanism at this point.
If you want a characters value, you need to use the ord method, as in a[5].ord or ?a.ord. ord is documented at http://ruby-doc.org/core-2.0.0/String.html#method-i-ord
The behavior of the ? operator and the String [] method when passed a single Fixnum changed at the same time in Ruby 1.9, with both returning a one-character string where they used to return a Fixnum.
As an aside, I can't find the documentation of the ? operator in the Literals/String section of the same official reference.
That is because of associativity/precedence. ?a[5] is interpreted as (?a)[5], not as ?(a[5]). I suppose you expected the latter, but it actually is the former.
In Ruby 1.8 ?a == 'a'[0]. Info about the ? operator (search for: "Integer and Floating Point Numbers")
Therefore you can get the value for a letter in the array a with:
a[5][0]
Whereas in Ruby > 1.9 use the method ord: a[5].ord
I am making a function that turns the first argument into a PHP var (useless, I know), and set it equal to the second argument. I'm trying to gsub! it to get rid of all the characters that can't be used in a PHP var. Here is what I have:
dvar = "$" + name.gsub!(/.?\/!#\#{}$%^&*()`~/, "") { |match| puts match }
I have the puts match there to make sure some of the characters were removed. name is a variable passed into a method in which this is its purpose. I am getting this error:
TypeError: can't convert nil into String
cVar at ./Web.rb:31
(root) at C:\Users\Andrew\Documents\NetBeansProjects\Web\lib\main.rb:13
Web.rb is the file this line is in, and main.rb is the file calling this method. How can I fix this?
EDIT: If I remove the ! in gsub!, it goes through, but the characters aren't removed.
Short answer
Use dvar = "$" + name.tr(".?\/!#\#{}$%^&*()``~", '')
Long answer
The problem you are facing is that the gsub! call is returning nil. You can't concatenate (+) a String with a nil.
That's happening because you have a malformed Regexp. You aren't escaping the special regex symbols, like $, * and ., just for a start. Also, the way it is now, gsub will only match if your string contains all that symbols in sequence. You should use the pipe (|) operator to make an OR like operation.
gsub! will also return nil if no substitutions happened.
See the documentation for gsub and gsub! here: http://ruby-doc.org/core/classes/String.html#M001186
I think you should replace gsub! with gsub. Do you really need name to change?
Example:
name = "m$var.name$$"
dvar = "$" + name.gsub!(/\$|\.|\*/, "") # $ or . or *
# dvar now contains $mvarname and name is mvarname
Your line, corrected:
dvar = "$" + name.gsub(/\.|\?|\/|\!|\#|\\|\#|\{|\}|\$|\%|\^|\&|\*|\(|\)|\`|\~/, "")
# some things shouldn't (or aren't needed to) be escaped, I don't remember them all right now
As J-_-L appointed, you could also use a character class ([]), that makes it a little clearer, I guess. Well, it's hard to mentally parse anyway.
dvar = "$" + name.gsub(/[\.\?\/\!\#\\\#\{\}\$\%\^\&\*\(\)\`\~]/, "")
But because what you are doing is simple character replacement, the best method is tr (again reminded by J-_-L!):
dvar = "$" + name.tr(".?\/!#\#{}$%^&*()`~", '')
Way easier to read and make modifications.
You cannot apply a second parameter
and a block to gsub (the block is ignored)
The regex is wrong, you forgot the
square brackets:
/[.?\/!#\#{}$%^&*()~]/`
Because your regex is wrong, it
didn't match anything and because
gsub! returns nil if nothing was
replaced, you get this strange nil no
method error
btw: you should use gsub not gsub! in
this case, because you are using the
return value (and not name itself) --
and the error would not have happened
i dont see what the block is for
just do
name = 'hello.?\/!##$%^&*()`~hello'
dvar = "$" + name.gsub(/\.|\?|\\|\/|\!|\#|\#|\{|\}|\$|\%|\^|\&|\*|\(|\)|\`|\~/, "")
puts dvar # => "$hellohello"
or use [] to denote OR
dvar = "$" + name.gsub(/[\.\?\\\/\!\#\\\#\{\}\$\%\^\&\*\(\)\`\~]/, "")
you have to escape the special characters and then OR them so it will remove them individually not just if they are all found together
also there is really no need to use gsub! to modify the string in place use the non mutator gsub() since you assign it to a new variable,
gsub! returns nil for which the operator + is not defined for stings, which gives you the no method error mentioned
It seems as the 'name' object is nil, you may be calling gsub! on nil which usually complains with a NoMethodError: private method gusb! called for nilNilClass, since I don't know the version of ruby you are using I am not sure if the error would be the same, but it's a good place to start looking at.