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  • Import web.go error after using goinstall

    - by Metropolis
    With halfdans advice, I was successfully able to use goinstall github.com/hoisie/web.go without any errors after installing git first. However, now when I try to compile the sample code given, go is not finding the web package. I get the error, main.go:4: can't find import: web On this code package main import ( "web" ) func hello(val string) string { return "hello " + val } func main() { web.Get("/(.*)", hello) web.Run("0.0.0.0:9999") } Is there something special I need to do in order for it to recognize the package? I found the package source at $GOROOT/src/pkg/github.com/hoisie/web.go/web. I tried github.com/hoisie/web.go/web as the import and it still did not like that.

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  • Learning the GO programming language and its prospects [closed]

    - by SHOUBHIK BOSE
    Possible Duplicate: What are the chances of Google's Go becoming a mainstream language? Recently I've started experimenting with The GO programming language by Google. Its a programmer-friendly language having the simplicity of Python. I was wondering whether companies other than Google would also start using Go for development, and if they do , what would be the prospects of being a Go programmer?

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  • Can "go" replace C++? [closed]

    - by iammilind
    I was reading wiki article about "go" programming language, where Bruce Eckel states: The complexity of C++ (even more complexity has been added in the new C++), and the resulting impact on productivity, is no longer justified. All the hoops that the C++ programmer had to jump through in order to use a C-compatible language make no sense anymore --they're just a waste of time and effort. Now, Go makes much more sense for the class of problems that C++ was originally intended to solve. Can go really replace C++(11) for new development in future? How about generic programming? I don't know go , but the amount of time (in)wasted in learning C++ seems to go in vain.

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  • Go import error while trying to import web.go package after using goinstall

    - by Metropolis
    With halfdans advice, I was successfully able to use goinstall github.com/hoisie/web.go without any errors after installing git first. However, now when I try to compile the sample code given, go is not finding the web package. I get the error, main.go:4: can't find import: web On this code package main import ( "web" ) func hello(val string) string { return "hello " + val } func main() { web.Get("/(.*)", hello) web.Run("0.0.0.0:9999") } Is there something special I need to do in order for it to recognize the package? I found the package source at $GOROOT/src/pkg/github.com/hoisie/web.go/web. I tried that path as the import and it still did not like that.

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  • Help me select a "Simpler" target to create a new language: .NET, LLVM, Go, Own VM

    - by mamcx
    Lets define "Simple". This is my first language. I have no previous experience I will not dedicate +4 years to learn it properly. I'm a professional software [developer], but as an amateur in this area, I want instant gratification. If the idea shows a future, I could rewrite it. I don't want to do everything from scratch. In fact, if there exists a way to get GO (for example), change its syntax, add some sugar, give some extra functions and leave intact everything else, that would be perfect! From the example of coffescript/scala I think is better to build on top of some rich runtime like .NET/GO so I don't need to rewrite everything. HOWEVER, if is better other way, no problem for the first try! I want it in a week. I need it in a week so it will really take a month. Then it truly takes 3 months. But I don't want to put more that 3 months on this. I could reduce the scope of my language, but I hope the tools will help me a lot... I want to build a new language. Similar to python, but typed. I wonder what to build it on top of. I like the idea of building on top of GO. To get their sane (IMHO) OO paradigm (I plan to do the same, using interfaces, not inheritance), get goroutines and some other stuff. In my naive thinking I imagine that spit another language could help me to debug it more easily. However, look like everyone is building on top of something like .NET (don't like Java), LLVM or make it own VM. I read http://createyourproglang.com/ (great!) and the part of the VM look "easy" to me. So, what I need is the proper criteria and question I need to know in advance to have a fair shot at make this.

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  • Go/Obj-C style interfaces with ability to extend compiled objects after initial release

    - by Skrylar
    I have a conceptual model for an object system which involves combining Go/Obj-C interfaces/protocols with being able to add virtual methods from any unit, not just the one which defines a class. The idea of this is to allow Ruby-ish open classes so you can take a minimalist approach to library development, and attach on small pieces of functionality as is actually needed by the whole program. Implementation of this involves a table of methods marked virtual in an RTTI table, which system functions are allowed to add to during module initialization. Upon typecasting an object to an interface, a Go-style lookup is done to create a vtable for that particular mapping and pass it off so you can have comparable performance to C/C++. In this case, methods may be added /afterwards/ which were not previously known and these new methods allow newer interfaces to be satisfied; while I like this idea because it seems like it would be very flexible (disregarding the potential for spaghetti code, which can happen with just about any model you use regardless). By wrapping the system calls for binding methods up in a set of clean C-compatible calls, one would also be able to integrate code with shared libraries and retain a decent amount of performance (Go does not do shared linking, and Objective-C does a dynamic lookup on each call.) Is there a valid use-case for this model that would make it worth the extra background plumbing? As much as this Dylan-style extensibility would be nice to have access to, I can't quite bring myself to a use case that would justify the overhead other than "it could make some kinds of code more extensible in future scenarios."

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  • Benefits of classic OOP over Go-like language

    - by tylerl
    I've been thinking a lot about language design and what elements would be necessary for an "ideal" programming language, and studying Google's Go has led me to question a lot of otherwise common knowledge. Specifically, Go seems to have all of the interesting benefits from object oriented programming without actually having any of the structure of an object oriented language. There are no classes, only structures; there is no class/structure inheritance -- only structure embedding. There aren't any hierarchies, no parent classes, no explicit interface implementations. Instead, type casting rules are based on a loose system similar to duck-typing, such that if a struct implements the necessary elements of a "Reader" or a "Request" or an "Encoding", then you can cast it and use it as one. Does such a system obsolete the concept of OOP? Or is there something about OOP as implemented in C++ and Java and C# that is inherently more capable, more maintainable, somehow more powerful that you have to give up when moving to a language like Go? What benefit do you have to give up to gain the simplicity that this new paradigm represents?

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  • ECS with Go - circular imports [migrated]

    - by Andreas
    I'm exploring both Go and Entity-Component-Systems. I understand how ECS works, and I'm trying to replicate what seems to be the go-to document of ECS, namely http://cowboyprogramming.com/2007/01/05/evolve-your-heirachy/ For performance, the document recommends to use static arrays of every component type. That is, not arrays of component interfaces (arrays of pointers). The problem with this in Go is circular imports. I have one package, ecs, which contains the definitions for Entity, Component and System types/interfaces as well as an EntityManager. Another package, ecs/components, contains the various components. Obviously, the ecs/components package depends on ecs. But, to declare arrays of specific components in EntityManager, ecs would depend on ecs/components, therefore creating a circular import. Is there any way of avoiding this? I am aware that normally a high level system should not depend on lower systems. I'm also want to point out that using an array of pointers is probably fast enough for my purposes, but I'm interested in possible workarounds (for future reference) Thank you for your help!

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  • Why is there a "new" keyword in Go?

    - by dystroy
    I'm still puzzled as why we have new in Go. &Thing{} is as clear and concise as new(Thing) to Go coders and it uses only constructs you often use elsewhere. It's also more extensible as you might change it to &Thing{3} or &Thing{Feets:7}. In my opinion, having a supplementary keyword is costly, it makes the language more complex and adds to what you must know. And it might mask to newcomers what's behind instantiating a struct. It also makes one more reserved word. So what's the reasoning behind new ? Is it something useful ? Should we use it ?

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  • D, Vala or Go for game development [on hold]

    - by Sheosi
    I'm looking forward to choose some compiled language for my 3D engine. The engine it's written in C++, however I would like to help coders by using a language which is good for games. I came with these three: Vala, D and Go. The engine is being made to write as less code as posible, also the "main" language it's going to be Lua so any of these will be the "advanced" one (mainly things which could affect performance or . Because of all this and the fact that I heard that Go is good for small projects I thought it would be a pretty good option, however it does not seems to be made (at least originally) for games and also some say I can have trouble with garbage collection in games. So what do you think? Do you have any experience with any of these three in games? How was it?

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  • Optimizing hash lookup & memory performance in Go

    - by Moishe
    As an exercise, I'm implementing HashLife in Go. In brief, HashLife works by memoizing nodes in a quadtree so that once a given node's value in the future has been calculated, it can just be looked up instead of being re-calculated. So eg. if you have a node at the 8x8 level, you remember it by its four children (each at the 2x2 level). So next time you see an 8x8 node, when you calculate the next generation, you first check if you've already seen a node with those same four children. This is extended up through all levels of the quadtree, which gives you some pretty amazing optimizations if eg. you're 10 levels above the leaves. Unsurprisingly, it looks like the perfmance crux of this is the lookup of nodes by child-node values. Currently I have a hashmap of {&upper_left_node,&upper_right_node,&lower_left_node,&lower_right_node} -> node So my lookup function is this: func FindNode(ul, ur, ll, lr *Node) *Node { var node *Node var ok bool nc := NodeChildren{ul, ur, ll, lr} node, ok = NodeMap[nc] if ok { return node } node = &Node{ul, ur, ll, lr, 0, ul.Level + 1, nil} NodeMap[nc] = node return node } What I'm trying to figure out is if the "nc := NodeChildren..." line causes a memory allocation each time the function is called. If it does, can I/should I move the declaration to the global scope and just modify the values each time this function is called? Or is there a more efficient way to do this? Any advice/feedback would be welcome. (even coding style nits; this is literally the first thing I've written in Go so I'd love any feedback)

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  • Go Big or Go Special

    - by Ajarn Mark Caldwell
    Watching Shark Tank tonight and the first presentation was by Mango Mango Preserves and it highlighted an interesting contrast in business trends today and how to capitalize on opportunities.  <Spoiler Alert> Even though every one of the sharks was raving about the product samples they tried, with two of them going for second and third servings, none of them made a deal to invest in the company.</Spoiler>  In fact, one of the sharks, Kevin O’Leary, kept ripping into the owners with statements to the effect that he thinks they are headed over a financial cliff because he felt their costs were way out of line and would be their downfall if they didn’t take action to radically cut costs. He said that he had previously owned a jams and jellies business and knew the cost ratios that you had to have to make it work.  I don’t doubt he knows exactly what he’s talking about and is 100% accurate…for doing business his way, which I’ll call “Go Big”.  But there’s a whole other way to do business today that would be ideal for these ladies to pursue. As I understand it, based on his level of success in various businesses and the fact that he is even in a position to be investing in other companies, Kevin’s approach is to go mass market (Go Big) and make hundreds of millions of dollars in sales (or something along that scale) while squeezing out every ounce of cost that you can to produce an acceptable margin.  But there is a very different way of making a very successful business these days, which is all about building a passionate and loyal community of customers that are rooting for your success and even actively trying to help you succeed by promoting your product or company (Go Special).  This capitalizes on the power of social media, niche marketing, and The Long Tail.  One of the most prolific writers about capitalizing on this trend is Seth Godin, and I hope that the founders of Mango Mango pick up a couple of his books (probably Purple Cow and Tribes would be good starts) or at least read his blog.  I think the adoration expressed by all of the sharks for the product is the biggest hint that they have a remarkable product and that they are perfect for this type of business approach. Both are completely valid business models, and it may certainly be that the scale at which Kevin O’Leary wants to conduct business where he invests his money is well beyond the long tail, but that doesn’t mean that there is not still a lot of money to be made there.  I wish them the best of luck with their endeavors!

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  • Why is there a "new" in Go?

    - by dystroy
    I'm still puzzled as why we have new in Go. When you want to instantiate a struct, you do t := Thing{} and, obviously, you can get a pointer to a new instance by doing t := &Thing{} But there's also this possibility : t := new(Thing) This last one seems a little alien to me. &Thing{} is as clear and concise as new(Thing) and it uses only constructs you often use elsewhere. It's also more extensible as you might change it to &Thing{3} or &Thing{Feets:7}. In my opinion, having a supplementary keyword is costly, it makes the language more complex and adds to what you must know. And it might mask to newcomers what's behind instantiating a struct. It also makes one more reserved word. So what's the reasoning behind new ? Is it something useful ? Should we use it ?

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  • Flood fill algorithm for Game of Go

    - by Jackson Borghi
    I'm having a hell of a time trying to figure out how to make captured stones disappear. I've read everywhere that I should use the flood fill algorithm, but I haven't had any luck with that so far. Any help would be amazing! Here is my code: package Go; import static java.lang.Math.*; import static stdlib.StdDraw.*; import java.awt.Color; public class Go2 { public static Color opposite(Color player) { if (player == WHITE) { return BLACK; } return WHITE; } public static void drawGame(Color[][] board) { Color[][][] unit = new Color[400][19][19]; for (int h = 0; h < 400; h++) { for (int x = 0; x < 19; x++) { for (int y = 0; y < 19; y++) { unit[h][x][y] = YELLOW; } } } setXscale(0, 19); setYscale(0, 19); clear(YELLOW); setPenColor(BLACK); line(0, 0, 0, 19); line(19, 19, 19, 0); line(0, 19, 19, 19); line(0, 0, 19, 0); for (double i = 0; i < 19; i++) { line(0.0, i, 19, i); line(i, 0.0, i, 19); } for (int x = 0; x < 19; x++) { for (int y = 0; y < 19; y++) { if (board[x][y] != YELLOW) { setPenColor(board[x][y]); filledCircle(x, y, 0.47); setPenColor(GRAY); circle(x, y, 0.47); } } } int h = 0; } public static void main(String[] args) { int px; int py; Color[][] temp = new Color[19][19]; Color[][] board = new Color[19][19]; Color player = WHITE; for (int i = 0; i < 19; i++) { for (int h = 0; h < 19; h++) { board[i][h] = YELLOW; temp[i][h] = YELLOW; } } while (true) { drawGame(board); while (!mousePressed()) { } px = (int) round(mouseX()); py = (int) round(mouseY()); board[px][py] = player; while (mousePressed()) { } floodFill(px, py, player, board, temp); System.out.print("XXXXX = "+ temp[px][py]); if (checkTemp(temp, board, px, py)) { for (int x = 0; x < 19; x++) { for (int y = 0; y < 19; y++) { if (temp[x][y] == GRAY) { board[x][y] = YELLOW; } } } } player = opposite(player); } } private static boolean checkTemp(Color[][] temp, Color[][] board, int x, int y) { if (x < 19 && x > -1 && y < 19 && y > -1) { if (temp[x + 1][y] == YELLOW || temp[x - 1][y] == YELLOW || temp[x][y - 1] == YELLOW || temp[x][y + 1] == YELLOW) { return false; } } if (x == 18) { if (temp[x - 1][y] == YELLOW || temp[x][y - 1] == YELLOW || temp[x][y + 1] == YELLOW) { return false; } } if (y == 18) { if (temp[x + 1][y] == YELLOW || temp[x - 1][y] == YELLOW || temp[x][y - 1] == YELLOW) { return false; } } if (y == 0) { if (temp[x + 1][y] == YELLOW || temp[x - 1][y] == YELLOW || temp[x][y + 1] == YELLOW) { return false; } } if (x == 0) { if (temp[x + 1][y] == YELLOW || temp[x][y - 1] == YELLOW || temp[x][y + 1] == YELLOW) { return false; } } else { if (x < 19) { if (temp[x + 1][y] == GRAY) { checkTemp(temp, board, x + 1, y); } } if (x >= 0) { if (temp[x - 1][y] == GRAY) { checkTemp(temp, board, x - 1, y); } } if (y < 19) { if (temp[x][y + 1] == GRAY) { checkTemp(temp, board, x, y + 1); } } if (y >= 0) { if (temp[x][y - 1] == GRAY) { checkTemp(temp, board, x, y - 1); } } } return true; } private static void floodFill(int x, int y, Color player, Color[][] board, Color[][] temp) { if (board[x][y] != player) { return; } else { temp[x][y] = GRAY; System.out.println("x = " + x + " y = " + y); if (x < 19) { floodFill(x + 1, y, player, board, temp); } if (x >= 0) { floodFill(x - 1, y, player, board, temp); } if (y < 19) { floodFill(x, y + 1, player, board, temp); } if (y >= 0) { floodFill(x, y - 1, player, board, temp); } } } }

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  • FloodFill Algorithm for Game of Go

    - by Jackson Borghi
    I'm having a hell of a time trying to figure out how to make captured stones disappear. I've read everywhere that I should use the FloodFill algorithm, but I havent had any luck with that so far. Any help would be amazing! Here is my code: package Go; import static java.lang.Math.; import static stdlib.StdDraw.; import java.awt.Color; public class Go2 { public static Color opposite(Color player) { if (player == WHITE) { return BLACK; } return WHITE; } public static void drawGame(Color[][] board) { Color[][][] unit = new Color[400][19][19]; for (int h = 0; h < 400; h++) { for (int x = 0; x < 19; x++) { for (int y = 0; y < 19; y++) { unit[h][x][y] = YELLOW; } } } setXscale(0, 19); setYscale(0, 19); clear(YELLOW); setPenColor(BLACK); line(0, 0, 0, 19); line(19, 19, 19, 0); line(0, 19, 19, 19); line(0, 0, 19, 0); for (double i = 0; i < 19; i++) { line(0.0, i, 19, i); line(i, 0.0, i, 19); } for (int x = 0; x < 19; x++) { for (int y = 0; y < 19; y++) { if (board[x][y] != YELLOW) { setPenColor(board[x][y]); filledCircle(x, y, 0.47); setPenColor(GRAY); circle(x, y, 0.47); } } } int h = 0; } public static void main(String[] args) { int px; int py; Color[][] temp = new Color[19][19]; Color[][] board = new Color[19][19]; Color player = WHITE; for (int i = 0; i < 19; i++) { for (int h = 0; h < 19; h++) { board[i][h] = YELLOW; temp[i][h] = YELLOW; } } while (true) { drawGame(board); while (!mousePressed()) { } px = (int) round(mouseX()); py = (int) round(mouseY()); board[px][py] = player; while (mousePressed()) { } floodFill(px, py, player, board, temp); System.out.print("XXXXX = "+ temp[px][py]); if (checkTemp(temp, board, px, py)) { for (int x = 0; x < 19; x++) { for (int y = 0; y < 19; y++) { if (temp[x][y] == GRAY) { board[x][y] = YELLOW; } } } } player = opposite(player); } } private static boolean checkTemp(Color[][] temp, Color[][] board, int x, int y) { if (x < 19 && x > -1 && y < 19 && y > -1) { if (temp[x + 1][y] == YELLOW || temp[x - 1][y] == YELLOW || temp[x][y - 1] == YELLOW || temp[x][y + 1] == YELLOW) { return false; } } if (x == 18) { if (temp[x - 1][y] == YELLOW || temp[x][y - 1] == YELLOW || temp[x][y + 1] == YELLOW) { return false; } } if (y == 18) { if (temp[x + 1][y] == YELLOW || temp[x - 1][y] == YELLOW || temp[x][y - 1] == YELLOW) { return false; } } if (y == 0) { if (temp[x + 1][y] == YELLOW || temp[x - 1][y] == YELLOW || temp[x][y + 1] == YELLOW) { return false; } } if (x == 0) { if (temp[x + 1][y] == YELLOW || temp[x][y - 1] == YELLOW || temp[x][y + 1] == YELLOW) { return false; } } else { if (x < 19) { if (temp[x + 1][y] == GRAY) { checkTemp(temp, board, x + 1, y); } } if (x >= 0) { if (temp[x - 1][y] == GRAY) { checkTemp(temp, board, x - 1, y); } } if (y < 19) { if (temp[x][y + 1] == GRAY) { checkTemp(temp, board, x, y + 1); } } if (y >= 0) { if (temp[x][y - 1] == GRAY) { checkTemp(temp, board, x, y - 1); } } } return true; } private static void floodFill(int x, int y, Color player, Color[][] board, Color[][] temp) { if (board[x][y] != player) { return; } else { temp[x][y] = GRAY; System.out.println("x = " + x + " y = " + y); if (x < 19) { floodFill(x + 1, y, player, board, temp); } if (x >= 0) { floodFill(x - 1, y, player, board, temp); } if (y < 19) { floodFill(x, y + 1, player, board, temp); } if (y >= 0) { floodFill(x, y - 1, player, board, temp); } } } }

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  • Go Big or Go Home

    - by user12601034
    For those who don’t know, Oracle sponsors a group called “OWL” – Oracle Women’s Leadership - and the purpose of the group is to create local and global opportunities that support, educate and empower current and future women leaders at Oracle. This week, I had the opportunity to attend the Denver OWL roadshow, and I was really impressed with the quality of speakers and interactions that I experienced. One theme that arose throughout the day was that of “Lean In.” In a nutshell, “Lean In” requires you to take advantage of the opportunities that you’re given. One of my personal mantras is “Go big or go home."  That is, if you’re not willing to give it your all, don’t do it at all. Regardless of how you phrase it, it’s a life lesson that I believe needs to be tossed in our face every so often simply, if for no other reason, to get our attention. You are given a finite amount of time in your life; in your job role; in your interactions with others. Do you make the most of the opportunities given to you every day? Or do you believe that life just happens, and you have to deal with whatever is handed to you? I have a challenge for you. Set aside any concerns or fears you have about something and Lean In. Make the most of an opportunity presented to you…or make your own opportunity! If you start with just one thing, you’ll start building a mindset to make the most of additional opportunities. Not only will you be better for leaning in, but I’m betting that those around you will be better for it as well.

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  • Go Big or Go Home

    - by Justin Kestelyn
    The Oracle Develop conference (#oracledevelop10), being co-located for the first time ever with JavaOne in San Francisco, is guaranteed to be the ultimate rush for developers this year. Where else can you go to learn about, interact with, and meet fellow devotees of the entire Oracle Development stack (welcome, Oracle Solaris)? This will also be the first time that the community space traditionally located at Oracle OpenWorld - and hosted by Oracle Technology Network, as always - will be present at the "developer" conference during this busy week. So, Oracle OpenWorld's loss is Oracle Develop's gain. And what a community space it will be: nearly 4,000 square feet for meeting space, contests and give-aways, consumption of various beverages, special speakers (Oracle ACEs among them, no doubt), and video-casting. The entire Oracle Technology Network crew will be on hand to "facilitate" your experience, of course. Even better, you can rub shoulders and share war stories with attendees from that "other" conference, JavaOne. (You have access to both conferences as a single package, so you may be having a conversation with yourself.) We call the whole enchilada "The Zone". As time goes on, we'll bring you more news about the activities described above, as well as OTN Night (which proves to be more raucous than ever), technical sessions and keynotes not to be missed, the unconference/open sessions, things to do at night, and more. In the meantime, stay in touch with us via Twitter or Oracle Mix.

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  • Add new types to Go

    - by nevalu
    I'm trying add new types for that been managed/used as in Go core types. To create new types is anything very interesting to validate data before of send it to a non-SQL DBMS or to check data from a form. Go uses univeral constants to define them at global level: var DateType = universe.DefineType("date", universePos, &dateType{}) In this case they're defined to be called from a package like types: var Date = &dateType{} I get these errors: test.go:58: o.lit undefined (cannot refer to unexported field lit) test.go:62: *dateType is not Type missing Pos() token.Position The code is based on: http://github.com/tav/go/blob/master/src/pkg/exp/eval/value.go http://github.com/tav/go/blob/master/src/pkg/exp/eval/type.go package main import ( "exp/eval" "fmt" // "go/token" ) // http://github.com/tav/go/blob/master/src/pkg/exp/eval/value.go type DateValue interface { eval.Value Get(*eval.Thread) string Set(*eval.Thread, string) } /* Date */ type dateV string func (v *dateV) String() string { return fmt.Sprint(*v) } func (v *dateV) Assign(t *eval.Thread, o eval.Value) { *v = dateV(o.(DateValue).Get(t)) } func (v *dateV) Get(*eval.Thread) string { return string(*v) } func (v *dateV) Set(t *eval.Thread, x string) { *v = dateV(x) } // http://github.com/tav/go/blob/master/src/pkg/exp/eval/type.go type Type interface { eval.Type // isDate returns true if this is a date type. isDate() bool } /* Common type */ type commonType struct{} // added func (commonType) isDate() bool { return false } /* Date */ type dateType struct { commonType } // * It should not be an universal constant //var universePos = token.Position{"<universe>", 0, 0, 0} // added //var DateType = universe.DefineType("date", universePos, &dateType{}) var Date = &dateType{} func (t *dateType) compat(o Type, conv bool) bool { t2, ok := o.lit().(*dateType) return ok && t == t2 } func (t *dateType) lit() Type { return t } func (t *dateType) isDate() bool { return true } func (t *dateType) String() string { return "<date>" } func (t *dateType) Zero() eval.Value { res := dateV("") return &res } /* Named types */ /* type NamedType struct { eval.NamedType Def Type }*/ type NamedType struct { // added // token.Position Name string // Underlying type. If incomplete is true, this will be nil. // If incomplete is false and this is still nil, then this is // a placeholder type representing an error. Def Type // True while this type is being defined. incomplete bool methods map[string]eval.Method } func (t *NamedType) isDate() bool { return t.Def.isDate() } /* *********************** */ func main() { print("foo") }

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  • What can Go chan do that a list cannot?

    - by alpav
    I want to know in which situation Go chan makes code much simpler than using list or queue or array that is usually available in all languages. As it was stated by Rob Pike in one of his speeches about Go lexer, Go channels help to organize data flow between structures that are not homomorphic. I am interested in a simple Go code sample with chan that becomes MUCH more complicated in another language (for example C#) where chan is not available. I am not interested in samples that use chan just to increase performance by avoiding waiting of data between generating list and consuming the list (which can be solved by chunking) or as a way to organize thread safe queue or thread-safe communication (which can be easily solved by locking primitives). I am interested in a sample that makes code simpler structurally disregarding size of data. If such sample does not exist then sample where size of data matters. I guess desired sample would contain bi-directional communication between generator and consumer. Also if someone could add tag [channel] to the list of available tags, that would be great.

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  • Go - Using a container/heap to implement a priority queue

    - by Seth Hoenig
    In the big picture, I'm trying to implement Dijkstra's algorithm using a priority queue. According to members of golang-nuts, the idiomatic way to do this in Go is to use the heap interface with a custom underlying data structure. So I have created Node.go and PQueue.go like so: //Node.go package pqueue type Node struct { row int col int myVal int sumVal int } func (n *Node) Init(r, c, mv, sv int) { n.row = r n.col = c n.myVal = mv n.sumVal = sv } func (n *Node) Equals(o *Node) bool { return n.row == o.row && n.col == o.col } And PQueue.go: // PQueue.go package pqueue import "container/vector" import "container/heap" type PQueue struct { data vector.Vector size int } func (pq *PQueue) Init() { heap.Init(pq) } func (pq *PQueue) IsEmpty() bool { return pq.size == 0 } func (pq *PQueue) Push(i interface{}) { heap.Push(pq, i) pq.size++ } func (pq *PQueue) Pop() interface{} { pq.size-- return heap.Pop(pq) } func (pq *PQueue) Len() int { return pq.size } func (pq *PQueue) Less(i, j int) bool { I := pq.data.At(i).(Node) J := pq.data.At(j).(Node) return (I.sumVal + I.myVal) < (J.sumVal + J.myVal) } func (pq *PQueue) Swap(i, j int) { temp := pq.data.At(i).(Node) pq.data.Set(i, pq.data.At(j).(Node)) pq.data.Set(j, temp) } And main.go: (the action is in SolveMatrix) // Euler 81 package main import "fmt" import "io/ioutil" import "strings" import "strconv" import "./pqueue" const MATSIZE = 5 const MATNAME = "matrix_small.txt" func main() { var matrix [MATSIZE][MATSIZE]int contents, err := ioutil.ReadFile(MATNAME) if err != nil { panic("FILE IO ERROR!") } inFileStr := string(contents) byrows := strings.Split(inFileStr, "\n", -1) for row := 0; row < MATSIZE; row++ { byrows[row] = (byrows[row])[0 : len(byrows[row])-1] bycols := strings.Split(byrows[row], ",", -1) for col := 0; col < MATSIZE; col++ { matrix[row][col], _ = strconv.Atoi(bycols[col]) } } PrintMatrix(matrix) sum, len := SolveMatrix(matrix) fmt.Printf("len: %d, sum: %d\n", len, sum) } func PrintMatrix(mat [MATSIZE][MATSIZE]int) { for r := 0; r < MATSIZE; r++ { for c := 0; c < MATSIZE; c++ { fmt.Printf("%d ", mat[r][c]) } fmt.Print("\n") } } func SolveMatrix(mat [MATSIZE][MATSIZE]int) (int, int) { var PQ pqueue.PQueue var firstNode pqueue.Node var endNode pqueue.Node msm1 := MATSIZE - 1 firstNode.Init(0, 0, mat[0][0], 0) endNode.Init(msm1, msm1, mat[msm1][msm1], 0) if PQ.IsEmpty() { // make compiler stfu about unused variable fmt.Print("empty") } PQ.Push(firstNode) // problem return 0, 0 } The problem is, upon compiling i get the error message: [~/Code/Euler/81] $ make 6g -o pqueue.6 Node.go PQueue.go 6g main.go main.go:58: implicit assignment of unexported field 'row' of pqueue.Node in function argument make: *** [all] Error 1 And commenting out the line PQ.Push(firstNode) does satisfy the compiler. But I don't understand why I'm getting the error message in the first place. Push doesn't modify the argument in any way.

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  • Why is go language so slow?

    - by oraz
    As we can see from The Computer Language Benchmarks Game: go is in average 10x slower then C go is 3x slower then Java !? How it can be bearing in mind that go compiler produces native code for execution? Immature compilers for go? Or there is some intrinsic problem with the go language?

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  • go programming POST FormValue can't be printed

    - by poor_programmer
    Before I being a bit of background, I am very new to go programming language. I am running go on Win 7, latest go package installer for windows. I'm not good at coding but I do like some challenge of learning a new language. I wanted to start learn Erlang but found go very interesting based on the GO I/O videos in youtube. I'm having problem with capturing POST form values in GO. I spend three hours yesterday to get go to print a POST form value in the browser and failed miserably. I don't know what I'm doing wrong, can anyone point me to the right direction? I can easily do this in another language like C#, PHP, VB, ASP, Rails etc. I have search the entire interweb and haven't found a working sample. Below is my sample code. Here is Index.html page {{ define "title" }}Homepage{{ end }} {{ define "content" }} <h1>My Homepage</h1> <p>Hello, and welcome to my homepage!</p> <form method="POST" action="/"> <p> Enter your name : <input type="text" name="username"> </P> <p> <button>Go</button> </form> <br /><br /> {{ end }} Here is the base page <!DOCTYPE html> <html lang="en"> <head> <title>{{ template "title" . }}</title> </head> <body> <section id="contents"> {{ template "content" . }} </section> <footer id="footer"> My homepage 2012 copy </footer> </body> </html> now some go code package main import ( "fmt" "http" "strings" "html/template" ) var index = template.Must(template.ParseFiles( "templates/_base.html", "templates/index.html", )) func GeneralHandler(w http.ResponseWriter, r *http.Request) { index.Execute(w, nil) if r.Method == "POST" { a := r.FormValue("username") fmt.Fprintf(w, "hi %s!",a); //<-- this variable does not rendered in the browser!!! } } func helloHandler(w http.ResponseWriter, r *http.Request) { remPartOfURL := r.URL.Path[len("/hello/"):] fmt.Fprintf(w, "Hello %s!", remPartOfURL) } func main() { http.HandleFunc("/", GeneralHandler) http.HandleFunc("/hello/", helloHandler) http.ListenAndServe("localhost:81", nil) } Thanks! PS: Very tedious to add four space before every line of code in stackoverflow especially when you are copy pasting. Didn't find it very user friendly or is there an easier way?

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  • Whats for to use GO

    - by Incognito
    I am interested in new language from Google, GO. I have checked the materials in the golang.com. And now want to use GO in practice. Please share any ideas whats for you are using GO. Or are there any open source GO projects that it would be possible to join?

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  • Go programming: How to get from cgo to exe

    - by Kawili-wili
    From a basic test program. . . package main /* #include <stdio.h> static void test() { printf("hello world"); } */ import "C" func main() { C.test(); } I do "cgo hello_cgo.go" and get: _cgo_.o _cgo_defun.c _cgo_gotypes.go hello_cgo.cgo1.go hello_cgo.cgo2.c How do I go about compiling from here to an exe?

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  • Wrapping FUSE from Go

    - by Matt Joiner
    I'm playing around with wrapping FUSE with Go. However I've come stuck with how to deal with struct fuse_operations. I can't seem to expose the operations struct by declaring type Operations C.struct_fuse_operations as the members are lower case, and my pure-Go sources would have to use C-hackery to set the members anyway. My first error in this case is "can't set getattr" in what looks to be the Go equivalent of a default copy constructor. My next attempt is to expose an interface that expects GetAttr, ReadLink etc, and then generate C.struct_fuse_operations and bind the function pointers to closures that call the given interface. This is what I've got (explanation continues after code): package fuse // #include <fuse.h> // #include <stdlib.h> import "C" import ( //"fmt" "os" "unsafe" ) type Operations interface { GetAttr(string, *os.FileInfo) int } func Main(args []string, ops Operations) int { argv := make([]*C.char, len(args) + 1) for i, s := range args { p := C.CString(s) defer C.free(unsafe.Pointer(p)) argv[i] = p } cop := new(C.struct_fuse_operations) cop.getattr = func(*C.char, *C.struct_stat) int {} argc := C.int(len(args)) return int(C.fuse_main_real(argc, &argv[0], cop, C.size_t(unsafe.Sizeof(cop)), nil)) } package main import ( "fmt" "fuse" "os" ) type CpfsOps struct { a int } func (me *CpfsOps) GetAttr(string, *os.FileInfo) int { return -1; } func main() { fmt.Println(os.Args) ops := &CpfsOps{} fmt.Println("fuse main returned", fuse.Main(os.Args, ops)) } This gives the following error: fuse.go:21[fuse.cgo1.go:23]: cannot use func literal (type func(*_Ctype_char, *_Ctype_struct_stat) int) as type *[0]uint8 in assignment I'm not sure what to pass to these members of C.struct_fuse_operations, and I've seen mention in a few places it's not possible to call from C back into Go code. If it is possible, what should I do? How can I provide the "default" values for interface functions that acts as though the corresponding C.struct_fuse_operations member is set to NULL?

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