I am working on an app which has the below code:
def app
#app ||= begin
if !::File.exist? options[:config]
abort "configuration #{options[:config]} not found"
end
app, myoptions = Rack::Builder.parse_file(self.options[:config], opt_parser)
self.myoptions.merge! myoptions
app
end
end
I am struggling to get my head around several parts of it..
#app||= begin...end
Does this mean that if #app does not exist the block is run?
app ,options = rack::builder
What does the comma do to it?
Please help
Your first assumptions was correct, it does say that if #app is nil, set it to whatever is returned in the block delimited with begin, end.
Regarding the comma, it works like this:
avar, bvar = "atest", "btest"
If you look at the source for Rack:Builder.parse_file then you will notice the last line
return app, options
So it is returning two values.
Hope that helps
#Craig-Taub ansewered the question,
I just want to add some notes:
Ruby commands are expressions which means they return value and you can assign them to variables.
You can read more about expressions and statements on Wikipedia and PragProg.
Second is that when you return more than one value in a code block, Ruby will wrap it into a simple array and return it to the caller.
That's why it works like that.
Related
#some_instance_var = Concurrent::Hash.new
(0...some.length).each do |idx|
fetch_requests[idx] = Concurrent::Promise.execute do
response = HTTP.get(EXTDATA_URL)
if response.status.success?
... # update #some_instance_var
end
# We're going to disregard GET failures here.
puts "I'm here"
end
end
Concurrent::Promise.all?(fetch_requests).execute.wait # let threads finish gathering all of the unique posts first
puts "how am i out already"
When I run this, the bottom line prints first, so it's not doing what I want of waiting for all the threads in the array to finish its work first, hence I keep getting an empty #some_instance_var to work with below this code. What am I writing wrong?
Never mind, I fixed this. That setup is correct, I just had to use the splat operator * for my fetch_requests array inside the all?().
Concurrent::Promise.all?(*fetch_requests).execute.wait
I guess it wanted multiple args instead of one array.
I'm trying to modify an existing lua script that cleans up subtitle data in Aegisub.
I want to add the ability to delete lines that contain the symbol "♪"
Here is the code I want to modify:
-- delete commented or empty lines
function noemptycom(subs,sel)
progress("Deleting commented/empty lines")
noecom_sel={}
for s=#sel,1,-1 do
line=subs[sel[s]]
if line.comment or line.text=="" then
for z,i in ipairs(noecom_sel) do noecom_sel[z]=i-1 end
subs.delete(sel[s])
else
table.insert(noecom_sel,sel[s])
end
end
return noecom_sel
end
I really have no idea what I'm doing here, but I know a little SQL and LUA apparently uses the IN keyword as well, so I tried modifying the IF line to this
if line.text in (♪) then
Needless to say, it didn't work. Is there a simple way to do this in LUA? I've seen some threads about the string.match() & string.find() functions, but I wouldn't know where to start trying to put that code together. What's the easiest way for someone with zero knowledge of Lua?
in is only used in the generic for loop. Your if line.text in (♪) then is no valid Lua syntax.
Something like
if line.comment or line.text == "" or line.text:find("\u{266A}") then
Should work.
In Lua every string have the string functions as methods attached.
So use gsub() on your string variable in loop like...
('Text with ♪ sign in text'):gsub('(♪)','note')
...thats replace the sign and output is...
Text with note sign in text
...instead of replacing it with 'note' an empty '' deletes it.
gsub() is returning 2 values.
First: The string with or without changes
Second: A number that tells how often the pattern matches
So second return value can be used for conditions or success.
( 0 stands for "pattern not found" )
So lets check above with...
local str,rc=('Text with strange ♪ sign in text'):gsub('(♪)','notation')
if rc~=0 then
print('Replaced ',rc,'times, changed to: ',str)
end
-- output
-- Replaced 1 times, changed to: Text with strange notation sign in text
And finally only detect, no change made...
local str,rc=('Text with strange ♪ sign in text'):gsub('(♪)','%1')
if rc~=0 then
print('Found ',rc,'times, Text is: ',str)
end
-- output is...
-- Found 1 times, Text is: Text with strange ♪ sign in text
The %1 holds what '(♪)' found.
So ♪ is replaced with ♪.
And only rc is used as a condition for further handling.
Actually I am writting a programming language in Lua. It was quite fun. I've wrote a bit of standard library (stack op and simple io). Then I've thought about labels. It would look like in assembly. While and for loop aren't funny in any bit so programming in that language can be quite challenging. Here are some requirements for this system:
Label stack (or array, dictionary) must be accessible from global context.
Jump instruction handler will be in separate file.
This is how my label-handling function look like:
function handleLabel(name,currentLine)
end
I have no idea how to implement this kind of magic. First I've thought about that:
LabelLineIDS = {}
Labels = {}
Labelamount = 1;
function handleLabel(name,currentLine)
LabelLineIDS[Labelamount]=currentline
Labels[Labelamount]=name
Labelamount=Labelamount+1
end
-- In file "jump.lua":
local function has_value (tab, val)
for index, value in ipairs(tab) do
if value == val then
return index
end
end
print ("Error: Label not defined.") -- Bail out.
os.exit(1)
end
local function _onlabel()
local labelName = globalparams --Globalparams variable contain parameters to each function, at the moment
--this will contain label name. It _can_ be nil.
return LabelLineIDS[has_value(Labels, labelName)]
end
CurrLine = _onlabel() --Currline - current line that get's parsed.
--1 command per one line.
But I'm unsure is this well written or even work. Can you give me idea how to parse labels in my programming language (and write jump functions)? Or if my code is pretty ok at the moment, can you help me to improve it?
Using line counter in my parser I've decided to implement gotos like we can see in BASIC. Thanks everyone for help.
When a user uses my application, at one point they will get an array of arrays, that looks like this:
results = [["value",25], ["value2",30]...]
The sub arrays could be larger, and will be in a similar format. I want to allow my users to write their own custom transform function that will take an array of arrays, and return either an array of arrays, a string, or a number. A function should look like this:
def user_transform_function(array_of_arrays)
# eval users code, only let them touch the array of arrays
end
Is there a safe way to sandbox this function and eval so a user could not try and execute malicious code? For example, no web callouts, not database callouts, and so on.
First, if you will use eval, it will never be safe. You can at least have a look in the direction of taint method.
What I would recommend is creating your own DSL for that. There is a great framework in Ruby: http://treetop.rubyforge.org/index.html. Of course, it will require some effort from your side, but from the user prospective I think it could be even better.
WARNING: I can not guarantee that this is truly safe!
You might be able to run it as a separate process and use ruby $SAFE, however this does not guarantee that what you get is safe, but it makes it harder to mess things up.
What you then would do is something like this:
script = "arr.map{|e| e+2}" #from the user.
require "json"
array = [1, 2, 3, 4]
begin
results = IO.popen("ruby -e 'require \"json\"; $SAFE=3; arr = JSON.parse(ARGV[0]); puts (#{script}).to_json' #{array.to_json}") do |io|
io.read
end
rescue Exception => e
puts "Ohh, good Sir/Mam, your script caused an error."
end
if results.include?("Insecure operation")
puts "Ohh, good Sir/Mam, you cannot do such a thing"
else
begin
a = JSON.parse(results)
results = a
rescue Exception => e
puts "Ohh, good Sir/Mam, something is wrong with the results."
puts results
end
end
conquer_the_world(results) if results.is_a?(Array)
do_not_conquer_the_world(results) unless results.is_a?(Array)
OR
You could do this, it appears:
def evaluate_user_script(script)
Thread.start {
$SAFE = 4
eval(script)
}
end
But again: I do not know how to get the data out of there.
I'm trying to get a handle on how OOP is done in Lua, and I thought I had a simple way to do it but it isn't working and I'm just not seeing the reason. Here's what I'm trying:
Person = { };
function Person:newPerson(inName)
print(inName);
p = { };
p.myName = inName;
function p:sayHello()
print ("Hello, my name is " .. self.myName);
end
return p;
end
Frank = Person.newPerson("Frank");
Frank:sayHello();
FYI, I'm working with the Corona SDK, although I am assuming that doesn't make a difference (except that's where print() comes from I believe). In any case, the part that's killing me is that inName is nil as reported by print(inName)... therefore, myName is obviously set to nil so calls to sayHello() fail (although they work fine if I hardcode a value for myName, which leads me to think the basic structure I'm trying is sound, but I've got to be missing something simple). It looks, as far as I can tell, like the value of inName is not being set when newPerson() is called, but I can't for the life of me figure out why; I don't see why it's not just like any other function call.
Any help would be appreciated. Thanks!
Remember that this:
function Person:newPerson(inName)
Is equivalent to this:
function Person.newPerson(self, inName)
Therefore, when you do this:
Person.newPerson("Frank");
You are passing one parameter to a function that expects two. You probably don't want newPerson to be created with :.
Try
Frank = Person:newPerson("Frank");