It is more an English question than a Coding question, but both are related :
Should we put an S in the name of array of things ? I want to know if it is just an opinion question or if there is a real English rule.
How to name an array of that array ?
Example 1
I have an object named Constraint. I want to create an array of that object. How should I name it ? ConstraintsArray or ConstraintArray ?
Answer
Do not use Hungarian Notation. Call it Constraints.
Example 2
How to name an array of that array ?
Thank you for your answers.
IMO, you should just call it "constraints", without the "array" prefix (referring the Clean code.. :) )
ConstraintsArray seems redundant in meaning.
You can use ConstraintArray or just Constraints.
I think it really depends on the coder himself. No real rules on variable on Grammar. :) . for me I like using singular form eg. ConstraintArray...
That is very much up to your personal style. I would not do it. A personArray is already a list of more than one person. You should know that.
But if the array objects are lists too it's a very different situation. Names like itemsDictionariesList, or repositoriesArray is something I used in my project.
Related
I am learning Ruby, reading few books, tutorials, foruns and so one... so, I am brand new to this.
I am trying to develop a stock system so I can learn doing.
My questions are the following:
I created the following to store transactions: (just few parts of the code)
transactions.push type: "BUY", date: Date.strptime(date.to_s, '%d/%m/%Y'), quantity: quantity, price: price.to_money(:BRL), fees: fees.to_money(:BRL)
And one colleague here suggested to create a Transaction class to store this.
So, for the next storage information that I had, I did:
#dividends_from_stock << DividendsFromStock.new(row["Approved"], row["Value"], row["Type"], row["Last Day With"], row["Payment Day"])
Now, FIRST question: which way is better? Hash in Array or Object in Array? And why?
This #dividends_from_stock is returned by the method 'dividends'.
I want to find all the dividends that were paid above a specific date:
puts ciel3.dividends.find_all {|dividend| Date.parse(dividend.last_day_with) > Date.parse('12/05/2014')}
I get the following:
#<DividendsFromStock:0x2785e60>
#<DividendsFromStock:0x2785410>
#<DividendsFromStock:0x2784a68>
#<DividendsFromStock:0x27840c0>
#<DividendsFromStock:0x1ec91f8>
#<DividendsFromStock:0x2797ce0>
#<DividendsFromStock:0x2797338>
#<DividendsFromStock:0x2796990>
Ok with this I am able to spot (I think) all the objects that has date higher than the 12/05/2014. But (SECOND question) how can I get the information regarding the 'value' (or other information) stored inside the objects?
Generally it is always better to define classes. Classes have names. They will help you understand what is going on when your program gets big. You can always see the class of each variable like this: var.class. If you use hashes everywhere, you will be confused because these calls will always return Hash. But if you define classes for things, you will see your class names.
Define methods in your classes that return the information you need. If you define a method called to_s, Ruby will call it behind the scenes on the object when you print it or use it in an interpolation (puts "Some #{var} here").
You probably want a first-class model of some kind to represent the concept of a trade/transaction and a list of transactions that serves as a ledger.
I'd advise steering closer to a database for this instead of manipulating toy objects in memory. Sequel can be a pretty simple ORM if used minimally, but ActiveRecord is often a lot more beginner friendly and has fewer sharp edges.
Using naked hashes or arrays is good for prototyping and seeing if something works in principle. Beyond that it's important to give things proper classes so you can relate them properly and start to refine how these things fit together.
I'd even start with TransactionHistory being a class derived from Array where you get all that functionality for free, then can go and add on custom things as necessary.
For example, you have a pretty gnarly interface to DividendsFromStock which could be cleaned up by having that format of row be accepted to the initialize function as-is.
Don't forget to write a to_s or inspect method for any custom classes you want to be able to print or have a look at. These are usually super simple to write and come in very handy when debugging.
thank you!
I will answer my question, based on the information provided by tadman and Ilya Vassilevsky (and also B. Seven).
1- It is better to create a class, and the objects. It will help me organize my code, and debug. Localize who is who and doing what. Also seems better to use with DB.
2- I am a little bit shamed with my question after figure out the solution. It is far simpler than I was thinking. Just needed two steps:
willpay = ciel3.dividends.find_all {|dividend| Date.parse(dividend.last_day_with) > Date.parse('10/09/2015')}
willpay.each do |dividend|
puts "#{ciel3.code} has approved #{dividend.type} on #{dividend.approved} and will pay by #{dividend.payment_day} the value of #{dividend.value.format} per share, for those that had the asset on #{dividend.last_day_with}"
puts
end
I was explaining to a friend a few days ago the concept or inheritance and containers.
He has very little programming knowledge so it was really just a friendly chat.
During the conversation he came to me with a question that i just couldn't answer.
"Why cant you just have an array of the top level class, and add anything to it"
I know this is a bad idea having being told so before by someone far smarter but for the life of me i couldn't remember why.
I mean we do it all the time with inheritance.
Say we have class animal which is parent of cat and dog. If we need a container of both of these we make the array of type animal.
So lets say we didn't have that inheritance link, couldn't we just use the base object class and have everything in the one container.
No specific programming language.
Syntactically, there is no problem with this. By declaring an array of a specific type, you are giving implicit information about the contents of that array. You could well declare a contain of Object instances, but it means you lose all the type information of the original class at compile-time.
It also means that each time you get an object out of the array at runtime, the only field instances and methods you know exist are the fields/methods of Object (which arguably is a compile time problem). To use any of the fields and methods of more specific subclasses of the object, you'd have to cast.
Alternatively, to find out the specific class at runtime you'd have to use features like reflection which are overkill for the majority of cases.
When you take elements out of the container you want to have some guarantees as to what can be done with them. If all elements of the container are returned as instances of Animal (remember here that instances of Dog are also instances of Animal) then you know that they can do all the things that Animals can do (which is more things than what all Objects can do).
Maybe, we do it in programming for the same reason as in Biology? Reptiles and Whales are animals, but they are quite different.
It depends on the situation, but without context, it's definitely okay in most (if not all) object-oriented languages to have an array of a base type (that is, as long as they follow all the substitution principles) containing various instances of different derived types.
Object arrays exist in certain cases in most languages. The problem is that whenever you want to use them, you need to remember what type they were, and stay casting them or whatever.
It also makes the code very horrible to follow and even more horrible to extend, not to mention error prone.
Plant myplant = new Plant();
listOfAnimals.Add(myplant);
would work if the list is object, but you'd get a compile time error if it was Animal.
I have question relating to implementation of arrays with Java+ANTLR combo. (I'm mainly talking about java/c style arrays).
So basically I'm asking how do you implement such feature, if there is such example already available or if someone could point me to anything that may point to solve it.
On other hand, I've searched a bit how would possible solution be. Main problem that I see
is that user may create arrays of various dimensions, even go crazy if he or she wants (like creating 5 dimension arrays or worse).
While grammar for something like this is fairly simple, like
new ID (INT (',' INT)* )
back end really gets involved a bit. As I said, user may input any number of dimensions, so array dimensions should be dynamically created. (at least as I see it, maybe I'm over complicating things?)
After searching I did found something that pretty much solves this problem perfectly, here is link to the question:
Is it possible to dynamically build a multi-dimensional array in Java?
Of course, my question is, is this viable example, it is a bit (to say at least), complicated? Is there more elegant solution to it?
Having that in mind, I was thinking maybe answer might be in the grounds of somehow transforming multidimensions
into more linear structure ? Could something like that be useful ? Simple search on stackoverflow pointed many solutions
to this, like:
Algorithm to convert a multi-dimensional array to a one-dimensional array
Would it be worth to search in that direction ?
Now, at the end, having in mind that arrays are really common feature in many languages, I must find it surprising that after searching ANTLR mailing list there is no similar question, which as I previously said leads me to believe that I'm maybe over complicating things ? (Unless I really suck at search?) I would really appreciate feedback.
Your syntax, if I'm not mistaken, corresponds to something like
new char 4,5,6,7
which is kind of strange. I expect that you really meant
new char[4,5,6,7]
However from a purely syntactic point of view, there's no reason not to just store the indices in an array and let the semantic analysis pass worry about it.
I have a very big C programming project that uses thousands of struct variables with this naming convention:
specificstruct->x = specificstruct->y + specificstruct->z
I want to do some heavy refactoring, namely converting most of these struct members to arrays. The code above would look like this:
specificstruct->x[i] = specificstruct->y[i] + specificstruct->z[i]
... and I don't feel like wasting an entire day on doing all this manually. Does anyone have a suitable regex in store?
EDIT: It is always the same struct, but the equations vary.
Thanks in advance!
Best regards,
P. Nilsson
I'm not sure about your particular case, but maybe Coccinelle can help you. It is a system for patching source code, based on some rules like "if x is an expression without function invocations, change x+x to 2*x" etc.
For a generalized approach something like this ought to do - the assumption is that you've got consistent spacing between your expressions
(.*?->.) = (.*?->.) \+ (.*?->.)
You can then write your new array structure as:
\1[i] = \2[i] + \3[i]
s/\(specificstruct->x\) = \(specificstruct->y\ )\+ \(specificstruct->z\)/\1[i] = \2[i] + \3[i]/g
If you're just looking for the name followed by -> then a single character, you could try
(?<struct>\w+)\s?->\s?(?<var>\w{1}) //single char after ->
(?<struct>\w+)\s?->\s?(?<var>\w+) //multiple char after ->
That way you have groups so you can compare the names before you do any replacements. The \s? helps to match even if you added spacing between some but not others.
I have created an array in the implementation of my class loginController. Now I want to use this array (with its objects) in another class of my project. What is the right way to import it?
You really need to specify the language.
In general, if the array is a member variable in one class, it's considered bad form to directly use it from another class. This violates the "encapsulation" idea that is quite the thing in object-oriented programming.
The preferred thing to do is often to add methods, called "getters" and "setters", to the class owning the array, or make it available by some other more structural means, which depend on the exact semantics and usage of the array. It might, for instance, not be required that outside users even know that it is an array.
There is no right way given this information. What is located in the array, only integers or strings/objects etc. Do you store objects of pointers to objects?
Passing the array is the sameway as passing any other object to a function
The general answer would be: declare it as public
It is not very good thing to do but as a beginner, you can start with that.