I am trying to only allow a person to see the page if their name is in the database. I figured the best way to go about it was to loop through all of the entries and check if it matches, if it does then display it and stop looping. I keep getting a blank page, any help?
get '/' do
user = "john"
num = DB[:users].all
for person in num do
if person[:name].to_s == user then
File.read('index.html')
break
else
"you're not authorized"
end
end
end
If I were to remove the line that says break within the if statement, I get this error:
NoMethodError at /
undefined method `bytesize' for #<Hash:0x007fcf60970a68>
file: utils.rb location: bytesize line: 369
The problem is that a for loop evaluates to nil (unless you break and supply a value to break), so your block is returning nil, so there's nothing to render.
But the real problem is that for is the wrong solution here. What you're trying to do is check if the Array DB[:users].all contains a Hash whose :name member equals user. You can use a loop for that, but in addition to for being rare in idiomatic Ruby code (Enumerable#each is preferred) it makes the intent of your code harder to understand. Instead, you could use Enumerable#find (the Array class includes the methods in the Enumerable module) like so:
get '/' do
username = "john"
users = DB[:users].all
matching_user = users.find do |user|
user[:name] == user
end
if matching_user
return File.read('index.html')
end
"you're not authorized"
end
...but since you don't actually care about the matching user—you only care if a matching user exists—it would be clearer to use Enumerable#any?, which just returns true or false:
get '/' do
username = "john"
users = DB[:users].all
if users.any? {|user| user[:name] == user }
return File.read('index.html')
end
"you're not authorized"
end
Edit: As #user846250 points out, it would be better to let the database do the work of checking if any matching users exist. Something like this:
get '/' do
username = "john"
if DB[:users].where(:name => username).empty?
return "you're not authorized"
end
File.read('index.html')
end
This is preferable because instead of loading all of the records from the database into Ruby (which is what DB[:users].all will do)—when you don't actually care about the data in any of them—Sequel will just ask the database if there are any matching records and then return true or false.
So I am working through test first and am a little stuck. Here is my code so far:
class Dictionary
attr_accessor :entries, :keywords, :item
def initialize
#entries = {}
end
def add(item)
item.each do |words, definition|
#entries[words] = definition
end
end
def keywords
#entries.keys
end
end#class
I am stuck at the rspec test right here:
it 'add keywords (without definition)' do
#d.add('fish')
#d.entries.should == {'fish' => nil}
#d.keywords.should == ['fish']
end
How can I switch my add method around to take either a key/value pair, or just a key with the value set to nil? The first test specifies that the hash is empty when it is created so I cant give it default values there.
One might check the type of the parameter passed to the add method. Whether it’s not an Enumerable, which is apparently a mixin included in Arrays, Hashes etc., just assign it’s value to nil:
def add(item)
case item
when Enumerable
item.each do |words, definition|
#entries[words] = definition
end
else
#entries[item] = nil
end
end
Please note that case uses “case equality” to check argument type.
If you are always passing Strings to the method, you could just have a default value for the second string... Something like the following:
def add(word, definition = nil)
#entries[word] = definition
end
So your code might look something like this:
class Dictionary
attr_accessor :entries, :keywords, :item
def initialize
#entries = {}
end
def add(word, definition = nil)
#entries[word] = definition
end
def keywords
#entries.keys
end
end#class
If you want multiple additions (i.e. add key: "word", with: "many", options: nil), that design might not work for you and you would need to create a solution that would work on the lines of what #mudasobwa suggested. Perhaps:
def add(word, definition = nil)
return #entries[word] = definition unless word.is_a?(Enumerable)
return #entries.update word if word.is_a?(Hash)
raise "What?!"
end
Update, as par request
I updated the method above to allow for words that aren't strings (as you pointed out).
When passing a hash to a method, it is considered as a single parameter.
Key => Value pairs are an implied hash, so when passing a hash to a method, the following are generally the same:
Hash.new.update key: :value
Hash.new.update({key: :value})
Consider the following:
def test(a,b = nil)
puts "a = #{a}"
puts "b = #{b}"
end
test "string"
# => a = string
# => b =
test "string", key: :value, key2: :value2
# => a = string
# => b = {:key=>:value, :key2=>:value2}
test key: :value, key2: :value2, "string"
# Wrong Ruby Syntax due to implied Hash, would raise exception:
# => SyntaxError: (irb):8: syntax error, unexpected '\n', expecting =>
test({key: :value, key2: :value2}, "string")
# correct syntax.
This is why, when you pass add 'fish' => 'aquatic', it's considered only one parameter, a hash - as opposed to add 'fish', 'aquatic' which passes two parameters to the method.
If your method must accept different types of parameters (strings, hashes, numerals, symbols, arrays), you will need to deal with each option in a different way.
This is why #mudasobwa suggested checking the first parameter's type. His solution is pretty decent.
My version is a bit shorter to code, but it runs on the same idea.
def add(word, definition = nil)
return #entries[word] = definition unless word.is_a?(Enumerable)
return #entries.update word if word.is_a?(Hash)
raise "What?!"
end
I was just reading a blog article and noticed that the author used tap in a snippet something like:
user = User.new.tap do |u|
u.username = "foobar"
u.save!
end
My question is what exactly is the benefit or advantage of using tap? Couldn't I just do:
user = User.new
user.username = "foobar"
user.save!
or better yet:
user = User.create! username: "foobar"
When readers encounter:
user = User.new
user.username = "foobar"
user.save!
they would have to follow all the three lines and then recognize that it is just creating an instance named user.
If it were:
user = User.new.tap do |u|
u.username = "foobar"
u.save!
end
then that would be immediately clear. A reader would not have to read what is inside the block to know that an instance user is created.
Another case to use tap is to make manipulation on object before returning it.
So instead of this:
def some_method
...
some_object.serialize
some_object
end
we can save extra line:
def some_method
...
some_object.tap{ |o| o.serialize }
end
In some situation this technique can save more then one line and make code more compact.
This can be useful with debugging a series of ActiveRecord chained scopes.
User
.active .tap { |users| puts "Users so far: #{users.size}" }
.non_admin .tap { |users| puts "Users so far: #{users.size}" }
.at_least_years_old(25) .tap { |users| puts "Users so far: #{users.size}" }
.residing_in('USA')
This makes it super easy to debug at any point in the chain without having to store anything in in a local variable nor requiring much altering of the original code.
And lastly, use it as a quick and unobtrusive way to debug without disrupting normal code execution:
def rockwell_retro_encabulate
provide_inverse_reactive_current
synchronize_cardinal_graham_meters
#result.tap(&method(:puts))
# Will debug `#result` just before returning it.
end
Using tap, as the blogger did, is simply a convenience method. It may have been overkill in your example, but in cases where you'd want to do a bunch of things with the user, tap can arguably provide a cleaner looking interface. So, perhaps it may be better in an example as follows:
user = User.new.tap do |u|
u.build_profile
u.process_credit_card
u.ship_out_item
u.send_email_confirmation
u.blahblahyougetmypoint
end
Using the above makes it easy to quickly see that all those methods are grouped together in that they all refer to the same object (the user in this example). The alternative would be:
user = User.new
user.build_profile
user.process_credit_card
user.ship_out_item
user.send_email_confirmation
user.blahblahyougetmypoint
Again, this is debatable - but the case can be made that the second version looks a little messier, and takes a little more human parsing to see that all the methods are being called on the same object.
If you wanted to return the user after setting the username you'd need to do
user = User.new
user.username = 'foobar'
user
With tap you could save that awkward return
User.new.tap do |user|
user.username = 'foobar'
end
It results in less-cluttered code as the scope of variable is limited only to the part where it is really needed. Also, the indentation within the block makes the code more readable by keeping relevant code together.
Description of tap says:
Yields self to the block, and then returns self. The primary purpose
of this method is to “tap into” a method chain, in order to perform
operations on intermediate results within the chain.
If we search rails source code for tap usage, we can find some interesting usages. Below are few items (not exhaustive list) that will give us few ideas on how to use them:
Append an element to an array based on certain conditions
%w(
annotations
...
routes
tmp
).tap { |arr|
arr << 'statistics' if Rake.application.current_scope.empty?
}.each do |task|
...
end
Initializing an array and returning it
[].tap do |msg|
msg << "EXPLAIN for: #{sql}"
...
msg << connection.explain(sql, bind)
end.join("\n")
As syntactic sugar to make code more readable - One can say, in below example, use of variables hash and server makes the intent of code clearer.
def select(*args, &block)
dup.tap { |hash| hash.select!(*args, &block) }
end
Initialize/invoke methods on newly created objects.
Rails::Server.new.tap do |server|
require APP_PATH
Dir.chdir(Rails.application.root)
server.start
end
Below is an example from test file
#pirate = Pirate.new.tap do |pirate|
pirate.catchphrase = "Don't call me!"
pirate.birds_attributes = [{:name => 'Bird1'},{:name => 'Bird2'}]
pirate.save!
end
To act on the result of a yield call without having to use a temporary variable.
yield.tap do |rendered_partial|
collection_cache.write(key, rendered_partial, cache_options)
end
Visualize your example within a function
def make_user(name)
user = User.new
user.username = name
user.save!
end
There is a big maintenance risk with that approach, basically the implicit return value.
In that code you do depend on save! returning the saved user. But if you use a different duck (or your current one evolves) you might get other stuff like a completion status report. Therefore changes to the duck might break the code, something that would not happen if you ensure the return value with a plain user or use tap.
I have seen accidents like this quite often, specially with functions where the return value is normally not used except for one dark buggy corner.
The implicit return value tends to be one of those things where newbies tend to break things adding new code after the last line without noticing the effect. They do not see what the above code really means:
def make_user(name)
user = User.new
user.username = name
return user.save! # notice something different now?
end
A variation on #sawa's answer:
As already noted, using tap helps figuring out the intent of your code (while not necessarily making it more compact).
The following two functions are equally long, but in the first one you have to read through the end to figure out why I initialized an empty Hash at the beginning.
def tapping1
# setting up a hash
h = {}
# working on it
h[:one] = 1
h[:two] = 2
# returning the hash
h
end
Here, on the other hand, you know right from the start that the hash being initialized will be the block's output (and, in this case, the function's return value).
def tapping2
# a hash will be returned at the end of this block;
# all work will occur inside
Hash.new.tap do |h|
h[:one] = 1
h[:two] = 2
end
end
It’s a helper for call chaining. It passes its object into the given block and, after the block finishes, returns the object:
an_object.tap do |o|
# do stuff with an_object, which is in o #
end ===> an_object
The benefit is that tap always returns the object it’s called on, even if the block returns some other result. Thus you can insert a tap block into the middle of an existing method pipeline without breaking the flow.
I would say that there is no advantage to using tap. The only potential benefit, as #sawa points out is, and I quote: "A reader would not have to read what is inside the block to know that an instance user is created." However, at that point the argument can be made that if you're doing non-simplistic record creation logic, your intent would be better communicated by extracting that logic into its own method.
I hold to the opinion that tap is an unnecessary burden on the readability of the code, and could be done without, or substituted with a better technique, like Extract Method.
While tap is a convenience method, it's also personal preference. Give tap a try. Then write some code without using tap, see if you like one way over another.
There is a tool called flog that measures how difficult it is to read a method. "The higher the score, the more pain the code is in."
def with_tap
user = User.new.tap do |u|
u.username = "foobar"
u.save!
end
end
def without_tap
user = User.new
user.username = "foobar"
user.save!
end
def using_create
user = User.create! username: "foobar"
end
and according on flog's result the method with tap is the most difficult to read (and I agree with it)
4.5: main#with_tap temp.rb:1-4
2.4: assignment
1.3: save!
1.3: new
1.1: branch
1.1: tap
3.1: main#without_tap temp.rb:8-11
2.2: assignment
1.1: new
1.1: save!
1.6: main#using_create temp.rb:14-16
1.1: assignment
1.1: create!
There could be number of uses and places where we may be able to use tap. So far I have only found following 2 uses of tap.
1) The primary purpose of this method is to tap into a method chain, in order to perform operations on intermediate results within the chain. i.e
(1..10).tap { |x| puts "original: #{x.inspect}" }.to_a.
tap { |x| puts "array: #{x.inspect}" }.
select { |x| x%2 == 0 }.
tap { |x| puts "evens: #{x.inspect}" }.
map { |x| x*x }.
tap { |x| puts "squares: #{x.inspect}" }
2) Did you ever find yourself calling a method on some object, and the return value not being what you wanted it to? Maybe you wanted to add an arbitrary value to a set of parameters stored in a hash. You update it with Hash.[], but you get back bar instead of the params hash, so you have to return it explicitly. i.e
def update_params(params)
params[:foo] = 'bar'
params
end
In order to overcome this situation here, tap method comes into play. Just call it on the object, then pass tap a block with the code that you wanted to run. The object will be yielded to the block, then be returned. i.e
def update_params(params)
params.tap {|p| p[:foo] = 'bar' }
end
There are dozens of other use cases, try finding them yourself :)
Source:
1) API Dock Object tap
2) five-ruby-methods-you-should-be-using
You're right: the use of tap in your example is kind of pointless and probably less clean than your alternatives.
As Rebitzele notes, tap is just a convenience method, often used to create a shorter reference to the current object.
One good use case for tap is for debugging: you can modify the object, print the current state, then continue modifying the object in the same block. See here for example: http://moonbase.rydia.net/mental/blog/programming/eavesdropping-on-expressions.
I occasionally like to use tap inside methods to conditionally return early while returning the current object otherwise.
You can make your codes more modular using tap, and can achieve a better management of local variables. For example, in the following code, you don't need to assign a local variable to the newly created object, in the scope of the method. Note that the block variable, u, is scoped within the block. It is actually one of the beauties of ruby code.
def a_method
...
name = "foobar"
...
return User.new.tap do |u|
u.username = name
u.save!
end
end
In rails we can use tap to whitelist parameters explicitly:
def client_params
params.require(:client).permit(:name).tap do |whitelist|
whitelist[:name] = params[:client][:name]
end
end
I will give another example which I have used. I have a method user_params which returns the params needed to save for the user (this is a Rails project)
def user_params
params.require(:user).permit(
:first_name,
:last_name,
:email,
:address_attributes
)
end
You can see I dont return anything but ruby return the output of the last line.
Then, after sometime, I needed to add a new attribute conditionally. So, I changed it to something like this:
def user_params
u_params = params.require(:user).permit(
:first_name,
:last_name,
:email,
:address_attributes
)
u_params[:time_zone] = address_timezone if u_params[:address_attributes]
u_params
end
Here we can use tap to remove the local variable and remove the return:
def user_params
params.require(:user).permit(
:first_name,
:last_name,
:email,
:address_attributes
).tap do |u_params|
u_params[:time_zone] = address_timezone if u_params[:address_attributes]
end
end
In the world where functional programming pattern is becoming a best practice (https://maryrosecook.com/blog/post/a-practical-introduction-to-functional-programming), you can see tap, as a map on a single value, indeed, to modify your data on a transformation chain.
transformed_array = array.map(&:first_transformation).map(&:second_transformation)
transformed_value = item.tap(&:first_transformation).tap(&:second_transformation)
No need to declare item multiple times here.
What is the difference?
The difference in terms of code readability is purely stylistic.
Code Walk through:
user = User.new.tap do |u|
u.username = "foobar"
u.save!
end
Key points:
Notice how the u variable is now used as block parameter?
After the block is done, the user variable should now point to a User ( with a username: ‘foobar’, and who is also saved).
It's just pleasant and easier to read.
API Documentation
Here’s an easy to read version of the source code:
class Object
def tap
yield self
self
end
end
For more info, see these links:
https://apidock.com/ruby/Object/tap
http://ruby-doc.org/core-2.2.3/Object.html#method-i-tap
Apart from the above answers, I have used tap in stubbing and mocking while writing RSpecs.
Scenario: When I have a complex query to stub and mock with multiple arguments which shouldn't go missed. The alternative here is to use receive_message_chain (but it lacks the details).
# Query
Product
.joins(:bill)
.where("products.availability = ?", 1)
.where("bills.status = ?", "paid")
.select("products.id", "bills.amount")
.first
# RSpecs
product_double = double('product')
expect(Product).to receive(:joins).with(:bill).and_return(product_double.tap do |product_scope|
expect(product_scope).to receive(:where).with("products.availability = ?", 1).and_return(product_scope)
expect(product_scope).to receive(:where).with("bills.status = ?", "paid").and_return(product_scope)
expect(product_scope).to receive(:select).with("products.id", "bills.amount").and_return(product_scope)
expect(product_scope).to receive(:first).and_return({ id: 1, amount: 100 })
end)
# Alternative way by using `receive_message_chain`
expect(Product).to receive_message_chain(:joins, :where, :where, :select).and_return({ id: 1, amount: 100 })
I am new to ruby. I tried to do a simple method(with parameter) call.
class MeowEncoder
def method(c)
puts c
end
end
print "please enter the thing you want"
s = gets.chomp()
MeowEncoder.method(s)
It is only passing parameter and prints it out. But the terminal keep giving me errors like
:MeowEncoder.rb:9: undefined method `toBinary' for MeowEncoder:Class (NoMethodError)
what is going on here?
I made some enhancement.
class MeowEncoder
def encode(n)
toBianry(?n)
puts ""
end
def toBinary(n)
if n < 2
print n
else
toBinary(n / 2)
print n % 2
end
end
end
o = MeowEncoder.new
print "please enter the thing you want: "
s = gets.chomp()
s.each_char{|c| o.encode(c)} #this doesn't work
o.toBinary(212) # this works
I made some enhancement here. I try to convert a char to its ASCII value then to its binary form. I can made the single toBinary works. But the Encode method also gave me same error. What happened?
You defined an instance method, but you're trying to call it on a class object. Try this:
MeowEncoder.new.method(s)
Also, method is a bad name for a method. It will cause a name clash.
To expand on Sergio's answer, if you actually wanted the method defined on the class, there are several ways to accomplish that, but the most straightforward is to prepend the method definition with self like so:
def self.method(c)
puts c
end
That will allow you to invoke the method the way you are currently.
The reason this works is, in the context of defining the method, self is set to the MeowEncoder class. It's equivalent to saying:
def MeowEncoder.method(c)
puts c
end
This is actually another valid way to declare class methods, but using self is better practice, as refactoring becomes easier if you ever change the name of your class.
Instead of each_char use each_byte and no need of encode method.
s.each_byte{|c| o.toBinary(c)}
Book (title, author)
Author (pseudonym, first_name, last_name)
Book_catalog => collection of books
methods
add_book(book)
remove_book(book)
borrow_book(borrower, book) => voeg boek toe aan borrower.books_borrowed
return_book(borrower, book) => verwijder boek uit borrower.books_borrowed
book_available?(book)
search(title) => geeft gevonden book-object terug (anders nil)
Book_borrowing
book (read-only), date_of_borrowing (read-only), date_of_return (read-only)
borrow_book(book_to_borrow) : #date_of_borrowing = systeem-datum+uur
return_book(book_to_return) : #date_of_return = systeem-datum+uur
Borrower
member_nbr, first_name, last_name, books_borrowed = collection of Book_borrowing
has_book_by_title(title) => geeft true of false terug
has_book(book) => geeft true of false terug
Person(first_name, last_name)
I have a method met1 that takes hash values as parameters.
For example: met1('abc' => 'xyz')
What should be the syntax when I define the method? Can it be something like this?
def met1(options)
puts options
end
I know the above syntax works. But how can I access the individual hash key and value inside the met1? (where key is abc and value is xyz?) Thank you!
Thats easy
met1("abc" => "xyz")
def met1(options)
puts options
# with key
puts options["abc"]
end
I assume you know what the options might contain in terms of keys right? if not,
def met1(options)
puts options.keys # options is the hash you passed it, use it like one
end
Your syntax is correct. simply use options['key'] (in case 'key' is a string) in your method. It's customary to use symbols as keys, so in your example:
met1(:abc => 'xyz')
def met1(options)
puts options[:abc]
end