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• blurry lines between web application context layer, service layer and data access layer in spring

  - by thenaglecode

  I Originally asked this question in SO but on advice I have moved the question here... I'll admit I'm a spring newbie, but you can correct me if I'm wrong, this one liner looks kinda fishy in a best practices sort of way: @RepositoryRestResource(collectionResourceRel="people"...) public interface PersonRepository extends PagingAndSortingRepository<Person, Long> For those who are unaware, the following does many things: It is an interface definition that can be registered in an application context as a jpa repository, automagically hooking up all the default CRUD operations within a persistence context (that is externally configured). and also configures default controller/request-mapping/handler functionality at the namespace "/people" relative to your configured dispatcher servlet-mapping. Here's my point. I just crossed 3 conceptual layers with one line of code! this feels against my seperation-of-concern instincts but i wanted to hear your opinion. And for the sake of being on a question and answer site, I would like to know whether there is a better way of seperating these different layers - Service, Data, Controllers - whilst maintaining as minimal configuration as possible

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• Multiple sites with the same codebase in Python

  - by Jimmy

  I am trying to run a large amount of sites which share about 90% of their code. They are simply designed to query an API and return the results. They will have a common userbase / database but will be configured slightly different and will have different CSS (perhaps even different templating). My initial idea was to run them as separate applications with a common library but I have read about the sites framework which would allow them to run from a single instance of Django which may help to reduce memory usage. https://docs.djangoproject.com/en/dev/ref/contrib/sites/ Is the site framework the right approach to a problem like this, and does it have real benefits over running separate applications? Initially I thought it was, but now I think otherwise. I have heard the following: Your SITE_ID is set in settings.py, so in order to have multiple sites, you need multiple settings.py configurations, which means multiple distinct processes/instances. You can of course share the code base between them, but each site will need a dedicated worker / WSGIDaemon to serve the site. This effectively removes any benefit of running multiple sites under one hood, if each site needs a UWSGI instance running. Alternative ideas of systems: https://github.com/iivvoo/django_layers https://github.com/shestera/django-multisite I don't know what route to be taking with this.

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• SQLite with two python processes accessing it: one reading, one writing

  - by BBnyc

  I'm developing a small system with two components: one polls data from an internet resource and translates it into sql data to persist it locally; the second one reads that sql data from the local instance and serves it via json and a restful api. I was originally planning to persist the data with postgresql, but because the application will have a very low-volume of data to store and traffic to serve, I thought that was overkill. Is SQLite up to the job? I love the idea of the small footprint and no need to maintain yet another sql server for this one task, but am concerned about concurrency. It seems that with write ahead logging enabled, concurrently reading and writing a SQLite database can happen without locking either process out of the database. Can a single SQLite instance sustain two concurrent processes accessing it, if only one reads and the other writes? I started writing the code but was wondering if this is a misapplication of SQLite.

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• Finding a way to simplify complex queries on legacy application

  - by glenatron

  I am working with an existing application built on Rails 3.1/MySql with much of the work taking place in a JavaScript interface, although the actual platforms are not tremendously relevant here, except in that they give context. The application is powerful, handles a reasonable amount of data and works well. As the number of customers using it and the complexity of the projects they create increases, however, we are starting to run into a few performance problems. As far as I can tell, the source of these problems is that the data represents a tree and it is very hard for ActiveRecord to deterministically know what data it should be retrieving. My model has many relationships like this: Project has_many Nodes has_many GlobalConditions Node has_one Parent has_many Nodes has_many WeightingFactors through NodeFactors has_many Tags through NodeTags GlobalCondition has_many Nodes ( referenced by Id, rather than replicating tree ) WeightingFactor has_many Nodes through NodeFactors Tag has_many Nodes through NodeTags The whole system has something in the region of thirty types which optionally hang off one or many nodes in the tree. My question is: What can I do to retrieve and construct this data faster? Having worked a lot with .Net, if I was in a similar situation there, I would look at building up a Stored Procedure to pull everything out of the database in one go but I would prefer to keep my logic in the application and from what I can tell it would be hard to take the queried data and build ActiveRecord objects from it without losing their integrity, which would cause more problems than it solves. It has also occurred to me that I could bunch the data up and send some of it across asynchronously, which would not improve performance but would improve the user perception of performance. However if sections of the data appeared after page load that could also be quite confusing. I am wondering whether it would be a useful strategy to make everything aware of it's parent project, so that one could pull all the records for that project and then build up the relationships later, but given the ubiquity of complex trees in day to day programming life I wouldn't be surprised if there were some better design patterns or standard approaches to this type of situation that I am not well versed in.

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• Flaws in my PHP development setup - sharing sources causing lags

  - by Wiktor

  I have following development setup for my PHP projects: Working station running on Windows 7 with PhpStorm IDE. GIT for version controlling. CentOS on virtual machine (VirtualBox) with Apache and MySQL (copy of production server). So far, I've been sharing project's source folders between host and guest systems and it was working quite well only really slow. The reason behind this is that Apache was reading files from remote folder (mounted locally). After doing some research, I found out that this set up can be improved by using disk mapping (Samba) instead of folder sharing. So I did that change. I configured my PhpStorm to automatically deploy files to mapped drive. Everything works like a charm now, except for one problem - when I change branches I need to synchronize project's local folder with the one on mapped drive and that takes time, a lot of time (like branching in SVN). Is there another way to handle this than just working on files directly on mapped drive?

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• What are some recommended video lectures for a non-CS student to prepare for the GRE CS subject test?

  - by aristos

  Well the title kinda explains all there is to explain. I'm a non-cs student and was preparing to apply PhD programs in applied mathematics. But for my senior thesis I've been reading lots of machine learning and pattern recognition literature and enjoying it a lot. I've taken lots of courses with statistics and stochastics content, which I think, would help me if I get accepted to a program with ML focus, but there are only two CS courses -introduction to programming- in my transcript and therefore I decided to take the CS subject test to increase my chances. Which courses do you think would be most essential to have a good result from CS subject test? I'm thinking of watching video lectures of them, so do you have any recommendations?

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• To implement registration page with Vaadin or not?

  - by JVerstry

  This is a tactical implementation question about usage of Vaadin or in some part of my application. Vaadin is a great framework to login users and implement sophisticated web applications with many pages. However, I think it is not very well suited to desgin pages to register new users for my application. Am I right? Am I am wrong? It seems to me that a simple HTML/CSS/Javascript login + email registration + confirmation email with confirmation link cannot be implemented easily with Vaadin. It seems like Vaadin would be overkill. Do you agree? Or am I missing something? I am looking for feedback from experienced Vaadin users.

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• String contains trailing zeroes when converted from decimal [migrated]

  - by Locke

  I've run into an unusual quirk in a program I'm writing, and I was trying to figure out if anyone knew the cause. Note that fixing the issue is easy enough. I just can't figure out why it is happening in the first place. I have a WinForms program written in VB.NET that is displaying a subset of data. It contains a few labels that show numeric values (the .Text property of the labels are being assigned directly from the Decimal values). These numbers are being returned by a DLL I wrote in C#. The DLL calls a webservice which initially returns the values in question. It returns one as a string, the other as a decimal (I don't have any control over the webservice, I just consume it). The DLL assigns these to properties on an object (both of which are decimals) then returns that object back to the WinForm program that called the DLL. Obviously, there's a lot of other data being consumed from the webservice, but no other operations are happening which could modify these properties. So, the short version is: WinForm requests a new Foo from the DLL. DLL creates object Foo. DLL calls webservice, which returns SomeOtherFoo. //Both Foo.Bar1 and Foo.Bar2 are decimals Foo.Bar1 = decimal.Parse(SomeOtherFoo.Bar1); //SomeOtherFoo.Bar1 is a string equal to "2.9000" Foo.Bar2 = SomeOtherFoo.Bar2; //SomeOtherFoo.Bar2 is a decimal equal to 2.9D DLL returns Foo to WinForm. WinForm.lblMockLabelName1.Text = Foo.Bar1 //Inspecting Foo.Bar1 indicates my value is 2.9D WinForm.lblMockLabelName2.Text = Foo.Bar2 //Inspecting Foo.Bar2 also indicates I'm 2.9D So, what's the quirk? WinForm.lblMockLabelName1.Text displays as "2.9000", whereas WinForm.lblMockLabelname2.Text displays as "2.9". Now, everything I know about C# and VB indicates that the format of the string which was initially parsed into the decimal should have no bearing on the outcome of a later decimal.ToString() operation called on the same decimal. I would expect that decimal.Parse(someDecimalString).ToString() would return the string without any trailing zeroes. Everything I find online seems to corroborate this (there are countless Stack Overflow questions asking exactly the opposite...how to keep the formatting from the initial parsing). At the moment, I've just removed the trailing zeroes from the initial string that gets parsed, which has hidden the quirk. However, I'd love to know why it happens in the first place.

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• Reasonable technological solutions to create CRM using .NET eventually Java

  - by user1825608

  My background(If it's too long, just skip it please ; ) ): I am Java programmer(because of demand): mostly teacher for other students, worked on few thesis for others, but during my journey I discovered that .NET and Microsoft's tools are on at least two levels higher than Java and its tools so I want to learn more about them. I programmed little bit on Windows Phone(NFC Tags, TCP Clients, guitar tuner using internal microphone, simple RSS), used WPF, integrated WPF with Windows Forms, Apple Bonjour(.NET), I have expierience with IP cameras and with unusal problems, I learn Android, but I don't like it at all. Problem: I was asked by my friend to create CRM for small new company. There will maximum 20 workers in the company working at computers in few cities in the country(Poland). They just want to store contracts with the clients and client's data. I am not sure what exacly they do but probably sell apartments so there will be at most few thousands of contracts to store in far future. Now I am totally new to CRM but I want to learn. I have few questions: Should the data be stored on a server in the company's building running 24/7 or cloud. If cloud which one? Should I use ASPX or WPF. I read one topic about it but as far as I know aspx sites can be viewed from every device with internet browser: tablets, phones(Android, WP, iOS) and computers at the same time- so the job is done once and for all(Am I right?), I don't know nothing about aspx. Can WPF be also used in manner that does not need to port it for other platforms?

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• mocha testing for the lazies, single key-press for all possible tests

  - by laggingreflex

  I have a batch file that lists all the test files I have and asks me which test I want to perform, like Test. [U]nit, [I]ntegration : i (user input) Integration. [A]ll, [2][U]serInteraction, [3][R]esultGeneration : u 2 User Interaction. Running "mocha integration\2userint.js" ... So essentially I have configured a batch "option" for each test file I have, which I can choose to run individually or all together. But adding and removing tests is a pain. Is there something that does this or anything like this automatically? Like reads all the files and asks me which file(s) I want to test. A GUI with checkboxes would be ultimate! but I'll take anything. I'm working in node.js

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• Getting the relational table data into XML recursively

  - by Tom

  I have levels of tables (Level1, Level2, Level3, ...) For simplicity, we'll say I have 3 levels. The rows in the higher level tables are parents of lower level table rows. The relationship does not skip levels however. E.g. Row1Level1 is parent of Row3Level2, Row2Level2 is parent of Row4Level3. Level(n-1)'s parent is always be in Level(n). Given these tables with data, I need to come up with a recursive function that generates an XML file to represent the relationship and the data. E.g. <data> <level levelid = 1 rowid=1> <level levelid = 2 rowid=3 /> </level> <level levelid = 2 rowid=2> <level levelid = 3 rowid=4 /> </level> </data> I would like help with coming up with a pseudo-code for this setup. This is what I have so far: XElement GetXMLData(Table table, string identifier, XElement data) { XElement xmlData = data; if (table != null) { foreach (row in the table) { // Get subordinate table Table subordinateTable = GetSubordinateTable(table); // Get the XML Data for the children of current row xmlData += GetXMLData(subordinateTable, row.Identifier, xmlData); } } return xmlData; }

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• How to present a stable data model in a public API that allows internal data structures to be changed without breaking the public view of the data?

  - by Max Palmer

  I am in the process of developing an application that allows users to write C# scripts. These scripts allow users to call selected methods and to access and manipulate data in a document. This works well, however, in the development version, scripts access the document's (internal) data structures directly. This means that if we were to change the internal data model/structure, there is a good chance that someone's script will no longer compile. We obviously want to prevent this breaking change from happening, but still want to allow the user to write sensible C# code (whilst not restricting how we develop our internal data model as a result). We therefore need to decouple our scripting API and its data structures from our internal methods and data structures. We've a few ideas as to how we might allow the user to access a what is effectively a stable public version of the document's internal data*, but I wanted to throw the question out there to someone who might have some real experience of this problem. NB our internal document's data structure is quite complex and it could be quite difficult to wrap. We know we want to expose as little as possible in our public API, especially as once it's out there, it's out there for good. Can anyone help? How do scripting languages / APIs decouple their public API and data structures from their internal data structures? Is there no real alternative to having to write a complex interaction layer? If we need to do this, what's a good approach or pattern for wrapping complex data structures that include nested objects, including collections? I've looked at the API facade pattern, which looks like it's trying to address these kinds of issues, but are there alternatives? *One idea is to build a data facade that is kept stable across versions of our application. The facade exposes a set of facade data objects that are used in the script code. These maintain backwards compatibility and wrap access to our internal document's data model.

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• How does copyrights apply to source code header files?

  - by Jim McKeeth

  It seems I heard that header files are not considered copyrightable since they can only be written one way (like a list of ingredients or facts). So a header file for a specific DLL will always look the same when written in a given programming language. Unfortunately I can't find any resources to back this up. So if a vendor provides an SDK with headers in one programming language, and then those headers are translated into another programming language by a third party. Does the 3rd party need permission from the vendor to provide the header translation? Who owns the copyright on the translation? Isn't it a derivative work still owned by the vendor, or is there no copyright, like a list of ingredients? Does this vary from jurisdiction to jurisdiction?

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• Reading mp3 metadata?

  - by Blaze

  I am planing on writing an application using Vala. Its purposed is to import mp3 files from a location and rename them if necessary. The renaming information should be provided by the ID3 tags in the mp3 file such as the title and the number of the song. My target platform is Ubuntu (Linux). As the question says, I am searching for how can I achieve this on Vala. I think this functionality might be provided by Gstreamer.

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• Using which technique does facebook and pininterest show images?

  - by manish

  If anybody has ever noticed that when you open a image in Facebook something like this happens:- suppose you are at your homepage on Facebook:- the URL is https://www.facebook.com/ now if you open a image it gets opened in new modal like window and URL changes to:- https://www.facebook.com/photo.php?fbid=10151125374887397&set=a.338008237396.161268.36922302396&type=1&theater As far as I know in any common case a modal overlay would have kept the url in the address bar the same , My question is how does facebook / pintrest achieve this behaviour of not re-loading the whole page but still achieving the change in the address bar. Is there any jquery or javascript plugin for this?

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• "Oracle Certified Expert, Java Platform, Enterprise Edition 6 Java Persistence API Developer" Preparation

  - by Matt

  I have been working with Hibernate for a fews years now, and I want to solidify and demonstrate my knowledge by taking the Oracle JPA certification, also known as: "Oracle Certified Expert, Java Platform, Enterprise Edition 6 Java Persistence API Developer (CX-310-094)" There is a training course provided by Oracle: "Building Database Driven Applications with JPA (SL-370-EE6)" But this costs $1800 and I think it would be overkill for my needs. Ideally, I would like a self study guide that will cover everything in the exam. I have looked for books and these seem like possibilities: Pro JPA 2: Mastering the Java Persistence API (Expert's Voice in Java Technology) and Beginning Java EE 6 with GlassFish 3 2nd Edition (Expert's Voice in Java Technology) But these aren't checklist type study guides as far as I am aware. I found the official SCJP study guide very useful, but I think the equivalent text for the JPA exam isn't out yet. If anyone has taken this exam, I would be grateful to hear how you prepared for it. Thanks!

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• How to write a product definition?

  - by Skarab

  I would like to learn how to write a software product definition. Therefore I am looking for online materials or books, which would help me to learn more about this topic. I would like to learn: what must be in what must not to be in how to make a product definition to sell internally the product finding balance between use case descriptions (the why), and feature descriptions (the how). ... I am aware that it is not something that can learn in 15 minutes but I think such a discussion could help me to have a good start.

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• Resources on learning to program in machine code?

  - by AceofSpades

  I'm a student, fresh into programming and loving it, from Java to C++ and down to C. I moved backwards to the barebones and thought to go further down to Assembly. But, to my surprise, a lot of people said it's not as fast as C and there is no use. They suggested learning either how to program a kernel or writing a C compiler. My dream is to learn to program in binary (machine code) or maybe program bare metal (program micro-controller physically) or write bios or boot loaders or something of that nature. The only possible thing I heard after so much research is that a hex editor is the closest thing to machine language I could find in this age and era. Are there other things I'm unaware of? Are there any resources to learn to program in machine code? Preferably on a 8-bit micro-controller/microprocessor. This question is similar to mine, but I'm interested in practical learning first and then understanding the theory.

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• Liskov substitution and abstract classes / strategy pattern

  - by Kolyunya

  I'm trying to follow LSP in practical programming. And I wonder if different constructors of subclasses violate it. It would be great to hear an explanation instead of just yes/no. Thanks much! P.S. If the answer is no, how do I make different strategies with different input without violating LSP? class IStrategy { public: virtual void use() = 0; }; class FooStrategy : public IStrategy { public: FooStrategy(A a, B b) { c = /* some operations with a, b */ } virtual void use() { std::cout << c; } private: C c; }; class BarStrategy : public IStrategy { public: BarStrategy(D d, E e) { f = /* some operations with d, e */ } virtual void use() { std::cout << f; } private: F f; };

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• Is it common to lie in job ads regarding the technologies in use?

  - by Desolate Planet

  Wanted: Experienced Delphi programmer to maintain ginormous legacy application and assist in migration to C# Later on, as the new hire settles into his role... "Oh, that C# migration? Yeah, we'd love to do that. But management is dead-set against it. Good thing you love Pascal, eh?" I've noticed quite a lot of this where I live (Scotland) and I'm not sure how common this is across IT: a company is using a legacy technology and they know that most developers will avoid them to keep mainstream technology on their resumes. So, they will put out a advertisement saying they are looking to move their product to some hip new tech (C#, Ruby, FORTRAN 99) and require someone who has exposure to both - but the migration is just a carrot on a stick, perpetually hung in front of the hungry developer as he spends each day maintaining the legacy app. I've experienced this myself, and heard far too many similar stories to the point where it seems like common practice. I've learned over time that every company has legacy problems of some sort, but I fail to see why they can't be honest about it. It should be common sense to any developer that the technology in place is there to support the business and not the other way round. Unless the technology is hurting the business in someway, I hardly see any just cause for reworking the software stack to be made up whatever is currently vogue in the industry. Would you say that this is commonplace? If so, how can I detect these kinds of leading advertisements beforehand?

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• Does the windows 8 store only support windows RT?

  - by Need4Sleep

  I'm in a project for creating a game engine and eventually a game, and we need ideas on how to get our game out into the internet. I had an idea with putting it onto the windows 8 store at a low cost(or free) in order to get the word out, but does the windows 8 store only support apps programmed in windows RT? our game will be built in C++ / OpenGL / GLEW / Actionscript / GLM / etc.. , so we wont be using any windows RT functionality at all.

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• About insertion sort and especially why it's said that copy is much faster than swap?

  - by Software Engeneering Learner

  From Lafore's "Data Structures and Algorithms in Java": (about insertion sort (which uses copy + shift instead of swap (used in bubble and selection sort))) However, a copy isn’t as time-consuming as a swap, so for random data this algo- rithm runs twice as fast as the bubble sort and faster than the selectionsort. Also author doesn't mention how time consuming shift is. From my POV copy is the simplest pointer assignment operation. While swap is 3x pointer assignment operations. Which doesn't take much time. Also shift of N elemtns is Nx pointer assignment operations. Please correct me if I'm wrong. Please explain, why what author says is true? I don't understand.

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• Suggestions for connecting .NET WPF GUI with Java SE Server aoo

  - by Sam Goldberg

  BACKGROUND We are building a Java (SE) trading application which will be monitoring market data and sending trade messages based on the market data, and also on user defined configuration parameters. We are planning to provide the user with a thin client, built in .NET (WPF) for managing the parameters, controlling the server behavior, and viewing the current state of the trading. The client doesn't need real-time updates; it will instead update the view once every few seconds (or whatever interval is configured by the user). The client has about 6 different operations it needs to perform with the server, for example: CRUD with configuration parameters query subset of the data receive updates of current positions from server It is possible that most of the different operations (except for receiving data) are just different flavors of managing the configuration parameters, but it's too early in our analysis for us to be sure. To connect the client with the server, we have been considering using: SOAP Web Service RESTful service building a custom TCP/IP based API (text or xml) (least preferred - but we use this approach with other applications we have) As best as I understand, pros and cons of the different web service flavors are: SOAP pro: totally automated in .NET (and Java), modifying server side interface require no code changes in communication layer, just running refresh on Web Service reference to regenerate the classes. con: more overhead in the communication layer sending more text, etc. We're not using J2EE container so maybe doesn't work so well with J2SE REST pro: lighter weight, less data. Has good .NET and Java support. (I don't have any real experience with this, so don't know what other benefits it has.) con: client will not be automatically aware if there are any new operations or properties added (?), so communication layer needs to be updated by developer if server interface changes. con: (both approaches) Server cannot really push updates to the client at regular intervals (?) (However, we won't mind if client polls the server to get updates.) QUESTION What are your opinions on the above options or suggestions for other ways to connect the 2 parts? (Ideally, we don't want to put much work into the communication layer, because it's not the significant part of the application so the more off-the-shelf and automated the better.)

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• Javascript form validation - what's lacking?

  - by box9

  I've tried out two javascript form validation frameworks - jQuery validation, and jQuery Tools validator - and I've found both of them lacking. jQuery validation lacks the clear separation between the concepts of "validating" and "displaying validation errors", and is highly inflexible when it comes to displaying dynamic error messages. jQuery Tools on the other hand lacks decent remote validation support (to check if a username exists for example). Even though jQuery validation supports remote validation, the built-in method requires the server to respond in a particular format. In both cases, any sort of asynchronous validation is a pain, as is defining rules for dependencies between multiple inputs. I'm thinking of rolling my own framework to address these shortcomings, but first I want to ask... have others experienced similar annoyances with javascript validation? What did you end up doing? What are some common validation requirements you've had which really should be catered for? And are there other, much better frameworks out there which I've missed? I'm looking primarily at jQuery-based frameworks, though well-implemented frameworks built on other libraries can still provide some useful ideas.

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• Were the first assemblers written in machine code?

  - by The111

  I am reading the book The Elements of Computing Systems: Building a Modern Computer from First Principles, which contains projects encompassing the build of a computer from boolean gates all the way to high level applications (in that order). The current project I'm working on is writing an assembler using a high level language of my choice, to translate from Hack assembly code to Hack machine code (Hack is the name of the hardware platform built in the previous chapters). Although the hardware has all been built in a simulator, I have tried to pretend that I am really constructing each level using only the tools available to me at that point in the real process. That said, it got me thinking. Using a high level language to write my assembler is certainly convenient, but for the very first assembler ever written (i.e. in history), wouldn't it need to be written in machine code, since that's all that existed at the time? And a correlated question... how about today? If a brand new CPU architecture comes out, with a brand new instruction set, and a brand new assembly syntax, how would the assembler be constructed? I'm assuming you could still use an existing high level language to generate binaries for the assembler program, since if you know the syntax of both the assembly and machine languages for your new platform, then the task of writing the assembler is really just a text analysis task and is not inherently related to that platform (i.e. needing to be written in that platform's machine language)... which is the very reason I am able to "cheat" while writing my Hack assembler in 2012, and use some preexisting high level language to help me out.

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