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  • python metaprogramming

    - by valya
    I'm trying to archive a task which turns out to be a bit complicated since I'm not very good at Python metaprogramming. I want to have a module locations with function get_location(name), which returns a class defined in a folder locations/ in the file with the name passed to function. Name of a class is something like NameLocation. So, my folder structure: program.py locations/ __init__.py first.py second.py program.py will be smth with with: from locations import get_location location = get_location('first') and the location is a class defined in first.py smth like this: from locations import Location # base class for all locations, defined in __init__ (?) class FirstLocation(Location): pass etc. Okay, I've tried a lot of import and getattribute statements but now I'm bored and surrender. How to archive such behaviour?

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  • grails metaprogramming

    - by Don
    Hi, My understanding is that there are two obvious places in a Grails app where one can do meta-programming: The init closure of Bootstrap.groovy The doWithDynamicMethods closure of a plugin The meta-programming I'm referring to here should be visible throughout the metaprogramming, typical examples include adding (or replacing) methods of 3rd party classes. String.metaClass.myCustomMethod = { /* implementation omitted */ } The disadvantage of (1), is that the metaprogramming won't be applied when the application is dynamically reloaded. The disadvantage of (2) is that I need to create and maintain an entire plugin just for the sake of a little metaprogramming. Is there a better place to do this kind of metaprogramming? Thanks, Don

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  • Best intro to C++ static metaprogramming?

    - by jwfearn
    Static metaprogramming (aka "template metaprogramming") is a great C++ technique that allows the execution of programs at compile-time. A light bulb went off in my head as soon as I read this canonical metaprogramming example: #include <iostream> using namespace std; template< int n > struct factorial { enum { ret = factorial< n - 1 >::ret * n }; }; template<> struct factorial< 0 > { enum { ret = 1 }; }; int main() { cout << "7! = " << factorial< 7 >::ret << endl; // 5040 return 0; } If one wants to learn more about C++ static metaprogramming, what are the best sources (books, websites, on-line courseware, whatever)?

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  • Language to learn metaprogramming

    - by Erup
    What's the best language (in terms of simplicity, readability and code elegancy) in your opinion, to learn and work with metaprogramming? I think metaprogramming is the "future of coding". Not saying that code will extinct, but we can see this scenario coming on new technologies.

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  • #AJIReport 16 | Jason Bock on Windows Runtime and Metaprogramming

    - by Jeff Julian
    This episode we sit down with Jason Bock to talk about Windows Runtime and his upcoming book on Metaprogramming. Jason has been a consultant at Magenic for the past 11 years. In this show, Jason walks us through how to get started with Windows RT and talks about what the experience is like deploying to the Windows Store. We get into the new frontier of device development and the restrictions that are in place to protect the users and other applications. Towards the end of the show we start talking about Jason's book on Metaprogramming that he is co-authoring with Kevin Hazard. Listen to the Show Site: http://www.jasonbock.net/ Book: Metaprogramming in .NET Twitter: @JasonBock

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  • Typed metaprogramming languages

    - by Jacques Carette
    I want to do some metaprogramming in a statically typed language, where both my programs and my meta-programs will be typed. I mean this in a strong sense: if my program generator compiles, I want the type system to be strong enough that only type-correct programs can be generated. As far as I know, only metaocaml can do this. (No, neither Template Haskell nor C++ templates fit the bill -- see this paper).

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  • Metaprogramming - self explanatory code - tutorials, articles, books

    - by elena
    Hello everybody, I am looking into improving my programming skils (actually I try to do my best to suck less each year, as our Jeff Atwood put it), so I was thinking into reading stuff about metaprogramming and self explanatory code. I am looking for something like an idiot's guide to this (free books for download, online resources). Also I want more than your average wiki page and also something language agnostic or preferably with Java examples. Do you know of such resources that will allow to efficiently put all of it into practice (I know experience has a lot to say in all of this but i kind of want to build experience avoiding the flow bad decisions - experience - good decisions)? EDIT: Something of the likes of this example from the Pragmatic Programmer: ...implement a mini-language to control a simple drawing package... The language consists of single-letter commands. Some commands are followed by a single number. For example, the following input would draw a rectangle: P 2 # select pen 2 D # pen down W 2 # draw west 2cm N 1 # then north 1 E 2 # then east 2 S 1 # then back south U # pen up Thank you!

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  • Getting template metaprogramming compile-time constants at runtime

    - by GMan - Save the Unicorns
    Background Consider the following: template <unsigned N> struct Fibonacci { enum { value = Fibonacci<N-1>::value + Fibonacci<N-2>::value }; }; template <> struct Fibonacci<1> { enum { value = 1 }; }; template <> struct Fibonacci<0> { enum { value = 0 }; }; This is a common example and we can get the value of a Fibonacci number as a compile-time constant: int main(void) { std::cout << "Fibonacci(15) = "; std::cout << Fibonacci<15>::value; std::cout << std::endl; } But you obviously cannot get the value at runtime: int main(void) { std::srand(static_cast<unsigned>(std::time(0))); // ensure the table exists up to a certain size // (even though the rest of the code won't work) static const unsigned fibbMax = 20; Fibonacci<fibbMax>::value; // get index into sequence unsigned fibb = std::rand() % fibbMax; std::cout << "Fibonacci(" << fibb << ") = "; std::cout << Fibonacci<fibb>::value; std::cout << std::endl; } Because fibb is not a compile-time constant. Question So my question is: What is the best way to peek into this table at run-time? The most obvious solution (and "solution" should be taken lightly), is to have a large switch statement: unsigned fibonacci(unsigned index) { switch (index) { case 0: return Fibonacci<0>::value; case 1: return Fibonacci<1>::value; case 2: return Fibonacci<2>::value; . . . case 20: return Fibonacci<20>::value; default: return fibonacci(index - 1) + fibonacci(index - 2); } } int main(void) { std::srand(static_cast<unsigned>(std::time(0))); static const unsigned fibbMax = 20; // get index into sequence unsigned fibb = std::rand() % fibbMax; std::cout << "Fibonacci(" << fibb << ") = "; std::cout << fibonacci(fibb); std::cout << std::endl; } But now the size of the table is very hard coded and it wouldn't be easy to expand it to say, 40. The only one I came up with that has a similiar method of query is this: template <int TableSize = 40> class FibonacciTable { public: enum { max = TableSize }; static unsigned get(unsigned index) { if (index == TableSize) { return Fibonacci<TableSize>::value; } else { // too far, pass downwards return FibonacciTable<TableSize - 1>::get(index); } } }; template <> class FibonacciTable<0> { public: enum { max = 0 }; static unsigned get(unsigned) { // doesn't matter, no where else to go. // must be 0, or the original value was // not in table return 0; } }; int main(void) { std::srand(static_cast<unsigned>(std::time(0))); // get index into sequence unsigned fibb = std::rand() % FibonacciTable<>::max; std::cout << "Fibonacci(" << fibb << ") = "; std::cout << FibonacciTable<>::get(fibb); std::cout << std::endl; } Which seems to work great. The only two problems I see are: Potentially large call stack, since calculating Fibonacci<2 requires we go through TableMax all the way to 2, and: If the value is outside of the table, it returns zero as opposed to calculating it. So is there something I am missing? It seems there should be a better way to pick out these values at runtime. A template metaprogramming version of a switch statement perhaps, that generates a switch statement up to a certain number? Thanks in advance.

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  • Cannot cout data [C++] [metaprogramming]

    - by atch
    Hi, Guys, reffering to last post I'm trying to output data while template is instantiated template <unsigned long N> struct binary { std::cout << N;//<---------------------------------I'M TRYING HERE static unsigned const value = binary<N/10>::value << 1 // prepend higher bits | N%10; // to lowest bit but I'm getting an error: 'Error 2 error C2886: 'std::cout' : symbol cannot be used in a member using- declaration ' Thanks for help P.S. And could anyone explain why actually I can't do that?

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  • Ruby Metaprogramming

    - by VP
    I'm trying to write a DSL that allows me to do Policy.name do author "Foo" reviewed_by "Bar" end The following code can almost process it: class Policy include Singleton def self.method_missing(name,&block) puts name puts "#{yield}" end def self.author(name) puts name end def self.reviewed_by(name) puts name end end Defining my method as class methods (self.method_name) i can access it using the following syntax: Policy.name do Policy.author "Foo" Policy.reviewed_by "Bar" end If i remove the "self" from the method names, and try to use my desired syntax, then i receive an error "Method not Found" in the Main so it could not find my function until the module Kernel. Its ok, i understand the error. But how can i fix it? How can i fix my class to make it work with my desired syntax that?

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  • replacing toString using Groovy metaprogramming

    - by Don
    In the following Groovy snippet, I attempt to replace both the hashCode and toString methods String.metaClass.toString = {-> "override" } String.metaClass.hashCode = {-> 22 } But when I test it out, only the replacement of hashCode works String s = "foo" println s.hashCode() // prints 22 println s.toString() // prints "foo" Is toString somehow a special case (possibly for security reasons)?

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  • Method For Making Methods: Easy Ruby Metaprogramming

    - by yar
    I have a bunch of methods like this in view helper def background "#e9eaec" end def footer_link_color "#836448" end I'd like these methods exposed to the view, but I'd prefer the helper to be a bit more concise. What's the best way to turn a hash, say, into methods (or something else)?

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  • Ruby: Dynamically calling available methods raising undefined method (metaprogramming)

    - by user94154
    I have an Activerecord object called Foo: Foo.attribute_names.each do |attribute| puts Foo.find(:all)[0].method(attribute.to_sym).call end Here I'm calling all attributes on this model (ie, querying for each column value). However, sometimes, I'll get an undefined method error. How can ActiveRecord::Base#attribute_names return an attribute name that when converted into its own method call, raises an undefined method error? Thank

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  • Python metaprogramming help

    - by Timmy
    im looking into mongoengine, and i wanted to make a class an "EmbeddedDocument" dynamically, so i do this def custom(cls): cls = type( cls.__name__, (EmbeddedDocument,), cls.__dict__.copy() ) cls.a = FloatField(required=True) cls.b = FloatField(required=True) return cls A = custom( A ) and tried it on some classes, but its not doing some of the base class's init or sumthing in BaseDocument def __init__(self, **values): self._data = {} # Assign initial values to instance for attr_name, attr_value in self._fields.items(): if attr_name in values: setattr(self, attr_name, values.pop(attr_name)) else: # Use default value if present value = getattr(self, attr_name, None) setattr(self, attr_name, value) but this never gets used, thus never setting ._data, and giving me errors. how do i do this?

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  • Avoiding class_eval in Ruby metaprogramming

    - by Peter
    I want to have a return_empty_set class method in Ruby, similar to the attr_reader methods. My proposed implementation is class Class def return_empty_set *list list.each do |x| class_eval "def #{x}; Set.new; end" end end end and example usage: class Foo return_empty_set :one end Foo.new.one # returns #<Set: {}> but resorting to a string seems like quite a hack. Is there a cleaner or better way to write this, perhaps avoiding class_eval? Or is this the best way to go?

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  • Metaprogramming ActiveRecord Rails

    - by Dimitar Vouldjeff
    Hi, I have the following code in my project`s lib directory module Pasta module ClassMethods def self.has_coordinates self.send :include, InstanceMethods end end module InstanceMethods def coordinates [longitude ||= 43.0, latitude ||= 25.0] end end ActiveRecord::Base.extend ClassMethods end And it should create a class method for ActiveRecord::Base - has_coordinates - which I can "assign" to models... But I receive the error undefined local variable or method 'has_coordinates' Thanks in advance!

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  • Ruby Metaprogramming

    - by Veerendra Manikonda
    I am having a method which returns the price of a given symbol and i am writing a test for that method. This is my test def setup @asset = NetAssetValue.new end def test_retrieve_price_for_symbol_YHOO assert_equal(33.987, @asset.retrieve_price_for_a_symbol('YHOO')) end def test_retrive_price_for_YHOO def self.retrieve_price_for_a_symbol(symbol) 33.77 end assert_equal(33.97, @asset.retrieve_price_for_a_symbol('YHOO')) end This is my method. def retrieve_price_for_a_symbol(symbol) symbol_price = { "YHOO" => 33.987, "UPS" => 35.345, "T" => 80.90 } raise Exception if(symbol_price[symbol].nil?) symbol_price[symbol] end I am trying to mock the retrieve_price_for_a_symbol method by writing same method in test class but when i call it, the call is happening to method in main class not in the test class. How do I add that method to meta class from test and how do i call it? Please help.

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  • Besides macros, are there any other metaprogramming techniques?

    - by mhr
    I'm making a programming language, and, having spent some time in Lisp/Scheme, I feel that my language should be malleable. Should I use macros, or is there something else I might/should use? Is malleable syntax even a good idea? Is it perhaps too powerful a concept? EDIT: In doing some research, I found fexprs. I don't really understand what these are. Help with that in an answer too please. EDIT2: Is it possible to have a language with macros/something-of-a-similar-nature without having s-expressions?

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