why is there a comma in this variable declaration:
// RinkebyBootnodes are the enode URLs of the P2P bootstrap nodes running on the
// Rinkeby test network.
var RinkebyBootnodes = []string{
"enode://a24ac7c5484ef4ed0c5eb2d36620ba4e4aa13b8c84684e1b4aab0cebea2ae45cb4d375b77eab56516d34bfbd3c1a833fc51296ff084b770b94fb9028c4d25ccf#52.169.42.101:30303", // IE
"enode://343149e4feefa15d882d9fe4ac7d88f885bd05ebb735e547f12e12080a9fa07c8014ca6fd7f373123488102fe5e34111f8509cf0b7de3f5b44339c9f25e87cb8#52.3.158.184:30303", // INFURA
}
I am talking about comma that goes here:
30303", // INFURA
it is the last character of the string array, and it has to go there, otherwise I get a compile error.
In C language you can't have commas at the end of curly braces {} , but in go you have to. Why ? And what does this comma mean?
Comma is an element splitter. Elements could be.written as in a row so in a column:
{1, 2, 3}
{
1,
2,
3,
}
It’s evident comma is unnecessary after the last element. Some languages require their absense like C, some - presence like Go, some allow both variants like Python. Sometimes it causes bugs like with JavaScript in old Internet Explorer.
Why do gophers decide to keep this comma? One of key principles of Go is visual simplicity and readability. This way all the strings look the same way. It’s easier to read them by eyes. Also suppose you add one more line - you have to edit previous one. And this creates visual noise in diff.
Thinking the same you get to the idea comma should not be in one liners. Because spoils readability as extra symbol.
Related
This produces newlines:
%(https://api.foursquare.com/v2/venues/search
?ll=80.914207,%2030.328466&radius=200
&v=20161201&m=foursquare&categoryId=4d4b7105d754a06374d81259
&intent=browse)
This produces spaces:
"https://api.foursquare.com/v2/venues/search
?ll=80.914207,%2030.328466&radius=200
&v=20161201&m=foursquare&categoryId=4d4b7105d754a06374d81259
&intent=browse"
This produces one string:
"https://api.foursquare.com/v2/venues/search"\
"?ll=80.914207,%2030.328466&radius=200"\
"&v=20161201&m=foursquare&categoryId=4d4b7105d754a06374d81259"\
"&intent=browse"
When I want to separate one string on multiple lines to read it better on screen, is it preferred to use the escape character?
My IDE complains that I should use single quoted strings rather than double quoted strings since there is no interpolation.
Normally you'd put something like this on one line, readability be damned, because the alternatives are going to be problematic. There's no way of declaring a string with whitespace ignored, but you can do this:
url = %w[ https://api.foursquare.com/v2/venues/search
?ll=80.914207,%2030.328466&radius=200
&v=20161201&m=foursquare&categoryId=4d4b7105d754a06374d81259
&intent=browse
].join
Where you explicitly remove the whitespace.
I'd actually suggest avoiding this whole mess by properly composing this URI:
uri = url("https://api.foursquare.com/v2/venues/search",
ll: [ 80.914207,30.328466 ],
radius: 200,
v: 20161201,
m: 'foursquare',
categoryId: '4d4b7105d754a06374d81259',
intent: 'browse'
)
Where you have some kind of helper function that properly encodes that using URI or other tools. By keeping your parameters as data, not as encoded strings, for as long as possible you make it easier to spot bugs as well as make last-second changes to them.
The answer by #tadman definitely suggests the proper way to do it; I’ll post another approach just for the sake of diversity:
query = "https://api.foursquare.com/v2/venues/search"
"?ll=80.914207,%2030.328466&radius=200"
"&v=20161201&m=foursquare&categoryId=4d4b7105d754a06374d81259"
"&intent=browse"
Yes, without any visible concatenation, 4 strings in quotes one by one in a row. This example won’t work in irb/pry (due to it’s REPL nature,) but the above is the most efficient way to concatenate strings in ruby without producing any intermediate result.
Contrived example to test in pry/irb:
value = "a" "b" "c" "d"
I need to validate that something is an Excel cell range in Ruby, i.e: "A4:A6". By looking at it, the requirement I am looking for is:
<Alphabetical, Capitalised><Integer>:<Integer><Alphabetical, Capitalised>
I am not sure how to form a RegExp for this.
I would appreciate a small explanation for a solution, as opposed to purely a solution.
A bonus would be to check that the range is restricted to within a row or column. I think this would be out of scope of Regular Expressions though.
I have tried /[A-Z]+[0-9]+:[A-Z]+[0-9]+/ this works but allows extra characters on the ends.
This does not work because it allows extra's to be added on to the beginning or end:
"HELLOAA3:A7".match(/\A[A-Z]+[0-9]+:[A-Z]+[0-9]+\z/) also returns a match, but is more on the right track.
How would I limit the number range to 10000?
How would I limit the number of characters to 3?
This is my solution:
(?:(?:\'?(?:\[(?<wbook>.+)\])?(?<sheet>.+?)\'?!)?(?<colabs>\$)?(?<col>[a-zA-Z]+)(?<rowabs>\$)?(?<row>\d+)(?::(?<col2abs>\$)?(?<col2>[a-zA-Z]+)(?<row2abs>\$)?(?<row2>\d+))?|(?<name>[A-Za-z]+[A-Za-z\d]*))
It includes named ranges, but the R1C1 notation is not supported.
The pattern is written in perl compatible regex dialect (i.e. can also be used with C#), I'm not familiar with Ruby, so I can't tell the difference, but you may want to look here: What is the difference between Regex syntax in Ruby vs Perl?
This will do both: match Excel range and that they must be same row or column. Stub
^([A-Z]+)(\d+):(\1\d+|[A-Z]+\2)$
A4:A6 // ok
A5:B10 // not ok
B5:Z5 // ok
AZ100:B100hello // not ok
The magic here is the back-reference group:
([A-Z]+)(\d+) -- column is in capture group 1, row in group 2
(\1\d+|[A-Z]+\2) -- the first column followed by any number; or
-- the first row preceded by any character
Example code:
let interestingNumbers = [
"Prime":[2,3,5,7,11,13],
"Fibonacci":[1,1,2,3,5,8],
"Square":[1,4,9,16,25]`,`
]
Question: after "Square:[1,4,9,16,25]", there is a comma(sample code from Apple Swift reference guide book), when I get rid of it, I didn't get any error messages from Xcode, is this just convention at all ? (I remember there is a nil after array or dictionary in objective-C
This is because a comma after the last element in a dictionary is optional.
Consider the simpler example:
let letters = ["A":1,
"B":2,
"C":3
]
A comma placed after the last element, "C":3, is acceptable, but optional.
I believe that there is no specific convention regarding the final comma - some may prefer it as it allows you to add items on following lines without modifying the above line to add the comma (makes source control review simpler). I often leave commas on the last element in an enum declaration for the same reason.
If you know you are likely to add more elements in the future, then having the comma would simplify the source diff in a code review (one added line instead of one removed line and two added lines). I would use the comma where you know you're going to add elements later, and omit in if the list of items is final.
I'm too ambitious or is there a way do this
to add a string if not present ?
and
remove a the same string if present?
Do all of this using Regex and avoid the if else statement
Here an example
I have string
"admin,artist,location_manager,event_manager"
so can the substring location_manager be added or removed with regards to above conditions
basically I'm looking to avoid the if else statement and do all of this plainly in regex
"admin,artist,location_manager,event_manager".test(/some_regex/)
The some_regex will remove location_manager from the string if present else it will add it
Am I over over ambitions
You will need to use some sort of logic.
str += ',location_manager' unless str.gsub!(/location_manager,/,'')
I'm assuming that if it's not present you append it to the end of the string
Regex will not actually add or remove anything in any language that I am aware of. It is simply used to match. You must use some other language construct (a regex based replacement function for example) to achieve this functionality. It would probably help to mention your specific language so as to get help from those users.
Here's one kinda off-the-wall solution. It doesn't use regexes, but it also doesn't use any if/else statements either. It's more academic than production-worthy.
Assumptions: Your string is a comma-separated list of titles, and that these are a unique set (no duplicates), and that order doesn't matter:
titles = Set.new(str.split(','))
#=> #<Set: {"admin", "artist", "location_manager", "event_manager"}>
titles_to_toggle = ["location_manager"]
#=> ["location_manager"]
titles ^= titles_to_toggle
#=> #<Set: {"admin", "artist", "event_manager"}>
titles ^= titles_to_toggle
#=> #<Set: {"location_manager", "admin", "artist", "event_manager"}>
titles.to_a.join(",")
#=> "location_manager,admin,artist,event_manager"
All this assumes that you're using a string as a kind of set. If so, you should probably just use a set. If not, and you actually need string-manipulation functions to operate on it, there's probably no way around except for using if-else, or a variant, such as the ternary operator, or unless, or Bergi's answer
Also worth noting regarding regex as a solution: Make sure you consider the edge cases. If 'location_manager' is in the middle of the string, will you remove the extraneous comma? Will you handle removing commas correctly if it's at the beginning or the end of the string? Will you correctly add commas when it's added? For these reasons treating a set as a set or array instead of a string makes more sense.
No. Regex can only match/test whether "a string" is present (or not). Then, the function you've used can do something based on that result, for example replace can remove a match.
Yet, you want to do two actions (each can be done with regex), remove if present and add if not. You can't execute them sequentially, because they overlap - you need to execute either the one or the other. This is where if-else structures (or ternary operators) come into play, and they are required if there is no library/native function that contains them to do exactly this job. I doubt there is one in Ruby.
If you want to avoid the if-else-statement (for one-liners or expressions), you can use the ternary operator. Or, you can use a labda expression returning the correct value:
# kind of pseudo code
string.replace(/location,?|$/, function($0) return $0 ? "" : ",location" )
This matches the string "location" (with optional comma) or the string end, and replaces that with nothing if a match was found or the string ",location" otherwise. I'm sure you can adapt this to Ruby.
to remove something matching a pattern is really easy:
(admin,?|artist,?|location_manager,?|event_manager,?)
then choose the string to replace the match -in your case an empty string- and pass everything to the replace method.
The other operation you suggested was more difficult to achieve with regex only. Maybe someone knows a better answer
I'm trying to make a simple Ruby regex to detect a JavaScript Declaration, but it fails.
Regex:
lines.each do |line|
unminifiedvar = /var [0-9a-zA-Z] = [0-9];/.match(line)
next if unminifiedvar == nil #no variable declarations on the line
#...
end
Testing Line:
var testvariable10 = 9;
A variable name can have more than one character, so you need a + after the character-set [...]. (Also, JS variable names can contain other characters besides alphanumerics.) A numeric literal can have more than one character, so you want a + on the RHS too.
More importantly, though, there are lots of other bits of flexibility that you'll find more painful to process with a regular expression. For instance, consider var x = 1+2+3; or var myString = "foo bar baz";. A variable declaration may span several lines. It need not end with a semicolon. It may have comments in the middle of it. And so on. Regular expressions are not really the right tool for this job.
Of course, it may happen that you're parsing code from a particular source with a very special structure and can guarantee that every declaration has the particular form you're looking for. In that case, go ahead, but if there's any danger that the nature of the code you're processing might change then you're going to be facing a painful problem that really isn't designed to be solved with regular expressions.
[EDITED about a day after writing, to fix a mistake kindly pointed out by "the Tin Man".]
You forgot the +, as in, more than one character for the variable name.
var [0-9a-zA-Z]+ = [0-9];
You may also want to add a + after the [0-9]. That way it can match multiple digits.
var [0-9a-zA-Z]+ = [0-9]+;
http://rubular.com/r/kPlNcGRaHA
Try /var [0-9a-zA-Z]+ = \d+;/
Without the +, [0-9a-zA-Z] will only match a single alphanumeric character. With +, it can match 1 or more alphanumeric characters.
By the way, to make it more robust, you may want to make it match any number of spaces between the tokens, not just exactly one space each. You may also want to make the semicolon at the end optional (because Javascript syntax doesn't require a semicolon). You might also want to make it always match against the whole line, not just a part of the line. That would be:
/\Avar\s+[0-9a-zA-Z]+\s*=\s*\d+;?\Z/
(There is a way to write [0-9a-zA-Z] more concisely, but it has slipped my memory; if someone else knows, feel free to edit this answer.)