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  • Cannot Generate ParameterSetMetadata While Programmatically Creating A Parameter Block

    - by Steven Murawski
    I'm trying to programmatically create a parameter block for a function ( along the lines of this blog post ). I'm starting with a CommandMetadata object (from an existing function). I can create the ParameterMetadata object and set things like the ParameterType, the name, as well as some attributes. The problem I'm running into is that when I use the GetParamBlock method of the ProxyCommand class, none of my attributes that I set in the Attributes collection of the ParameterMetadata are generated. The problem this causes is that when the GetParamBlock is called, the new parameter is not annotated with the appropriate Parameter attribute. Example: function test { [CmdletBinding()] param ( [Parameter()] $InitialParameter) Write-Host "I don't matter." } $MetaData = New-Object System.Management.Automation.CommandMetaData (get-command test) $NewParameter = New-Object System.Management.Automation.ParameterMetadata 'NewParameter' $NewParameter.ParameterType = [string[]] $Attribute = New-Object System.Management.Automation.ParameterAttribute $Attribute.Position = 1 $Attribute.Mandatory = $true $Attribute.ValueFromPipeline = $true $NewParameter.Attributes.Add($Attribute) $MetaData.Parameters.Add('NewParameter', $NewParameter) [System.Management.Automation.ProxyCommand]::GetParamBlock($MetaData)

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  • Checking if a function has C-linkage at compile-time

    - by scjohnno
    Is there any way to check if a given function is declared with C-linkage (that is, with extern "C") at compile-time? I am developing a plugin system. Each plugin can supply factory functions to the plugin-loading code. However, this has to be done via name (and subsequent use of GetProcAddress or dlsym). This requires that the functions be declared with C-linkage so as to prevent name-mangling. It would be nice to be able to throw a compiler error if the referred-to function is declared with C++-linkage (as opposed to finding out at runtime when a function with that name does not exist). Here's a simplified example of what I mean: extern "C" void my_func() { } void my_other_func() { } // Replace this struct with one that actually works template<typename T> struct is_c_linkage { static const bool value = true; }; template<typename T> void assertCLinkage(T *func) { static_assert(is_c_linkage<T>::value, "Supplied function does not have C-linkage"); } int main() { assertCLinkage(my_func); // Should compile assertCLinkage(my_other_func); // Should NOT compile } Thanks.

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  • How do I call +class methods in Objective C without referencing the class?

    - by TimM
    I have a series of "policy" objects which I thought would be convenient to implement as class methods on a set of policy classes. I have specified a protocol for this, and created classes to conform to (just one shown below) @protocol Counter +(NSInteger) countFor: (Model *)model; @end @interface CurrentListCounter : NSObject <Counter> +(NSInteger) countFor: (Model *)model; @end I then have an array of the classes that conform to this protocol (like CurrentListCounter does) +(NSArray *) availableCounters { return [[[NSArray alloc] initWithObjects: [CurrentListCounter class],[AllListsCounter class], nil] autorelease]; } Notice how I am using the classes like objects (and this might be my problem - in Smalltalk classes are objects like everything else - I'm not sure if they are in Objective-C?) My exact problem is when I want to call the method when I take one of the policy objects out of the array: id<Counter> counter = [[MyModel availableCounters] objectAtIndex: self.index]; return [counter countFor: self]; I get a warning on the return statement - it says -countFor: not found in protocol (so its assuming its an instance method where I want to call a class method). However as the objects in my array are instances of class, they are now like instance methods (or conceptually they should be). Is there a magic way to call class methods? Or is this just a bad idea and I should just create instances of my policy objects (and not use class methods)?

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  • Programming tutorials for people with zero experience

    - by www.aegisub.net
    A friend of mine is interested in learning how to program computers, but she knows nothing about programming. I suggested that Python might be a good language to start with, but after some googling, I couldn't find any tutorials that covered both programming and Python in an adequate way. I don't want her to go through the tiresome "learn algorithms in pseudocode first" routine. Instead, I'd like a tutorial that will explain the basic ideas while working towards a real goal, e.g. a very simple console game. Does anyone know of any such tutorials? Do you think that I'm mistaken in how I'm handling this? Is Python a bad choice? I know that something like C, C++ or Java won't work - too many details will be very counterproductive. On the other hand, I think that Lisp might be too mathematical and abstract. Python, on the other hand, will let her even do something like coding primitive graphical games in a short period of time.

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  • Should this work?

    - by Noah Roberts
    I am trying to specialize a metafunction upon a type that has a function pointer as one of its parameters. The code compiles just fine but it will simply not match the type. #include <iostream> #include <boost/mpl/bool.hpp> #include <boost/mpl/identity.hpp> template < typename CONT, typename NAME, typename TYPE, TYPE (CONT::*getter)() const, void (CONT::*setter)(TYPE const&) > struct metafield_fun {}; struct test_field {}; struct test { int testing() const { return 5; } void testing(int const&) {} }; template < typename T > struct field_writable : boost::mpl::identity<T> {}; template < typename CONT, typename NAME, typename TYPE, TYPE (CONT::*getter)() const > struct field_writable< metafield_fun<CONT,NAME,TYPE,getter,0> > : boost::mpl::false_ {}; typedef metafield_fun<test, test_field, int, &test::testing, 0> unwritable; int main() { std::cout << typeid(field_writable<unwritable>::type).name() << std::endl; std::cin.get(); } Output is always the type passed in, never bool_.

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  • Creating serializeable unique compile-time identifiers for arbitrary UDT's.

    - by Endiannes
    I would like a generic way to create unique compile-time identifiers for any C++ user defined types. for example: unique_id<my_type>::value == 0 // true unique_id<other_type>::value == 1 // true I've managed to implement something like this using preprocessor meta programming, the problem is, serialization is not consistent. For instance if the class template unique_id is instantiated with other_type first, then any serialization in previous revisions of my program will be invalidated. I've searched for solutions to this problem, and found several ways to implement this with non-consistent serialization if the unique values are compile-time constants. If RTTI or similar methods, like boost::sp_typeinfo are used, then the unique values are obviously not compile-time constants and extra overhead is present. An ad-hoc solution to this problem would be, instantiating all of the unique_id's in a separate header in the correct order, but this causes additional maintenance and boilerplate code, which is not different than using an enum unique_id{my_type, other_type};. A good solution to this problem would be using user-defined literals, unfortunately, as far as I know, no compiler supports them at this moment. The syntax would be 'my_type'_id; 'other_type'_id; with udl's. I'm hoping somebody knows a trick that allows implementing serialize-able unique identifiers in C++ with the current standard (C++03/C++0x), I would be happy if it works with the latest stable MSVC and GNU-G++ compilers, although I expect if there is a solution, it's not portable.

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  • In the generic programming/TMP world what exactly is a model / a policy and a "concept" ?

    - by Hassan Syed
    I'd like to know the precise yet succinct definitions of these three concepts in one place. The quality of the answer should depend on the following two points. Show a simple code snippet to show how and what the concept/technique is used for. Be simple enough to understand so that a programmer without any exposure to this area can grasp it. Note: There are probably many correct answers since each concept has many different facets. If there are a lot of good answers I will eventually turn the question into CW and aggregate the answers. -- Post Accept Edit -- Boost has a nice article on generic programming concepts

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  • Heroku DJango app development on Windows

    - by Cliff
    I'm trying to start a Django app on Heroku using Windows and I'm getting stuck on the following error when I try to pip install psycopg2: Downloading/unpacking psycopg2 Downloading psycopg2-2.4.5.tar.gz (719Kb): 719Kb downloaded Running setup.py egg_info for package psycopg2 Error: pg_config executable not found. Please add the directory containing pg_config to the PATH or specify the full executable path with the option: python setup.py build_ext --pg-config /path/to/pg_config build ... or with the pg_config option in 'setup.cfg'. Complete output from command python setup.py egg_info: running egg_info creating pip-egg-info\psycopg2.egg-info writing pip-egg-info\psycopg2.egg-info\PKG-INFO writing top-level names to pip-egg-info\psycopg2.egg-info\top_level.txt writing dependency_links to pip-egg-info\psycopg2.egg-info\dependency_links.txt writing manifest file 'pip-egg-info\psycopg2.egg-info\SOURCES.txt' warning: manifest_maker: standard file '-c' not found I've googled the error and it seems you need libpq-dev python-dev as dependencies for postgres under Python. I also turned up a link that says you gt into trouble if you don't have the postgres bin folder in your Path so I installed Postgres manually and tried again. This time I get: error: Unable to find vcvarsall.bat I am still a python N00b so I am lost. Could someone point me in a general direction?

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  • How can I write a function template for all types with a particular type trait?

    - by TC
    Consider the following example: struct Scanner { template <typename T> T get(); }; template <> string Scanner::get() { return string("string"); } template <> int Scanner::get() { return 10; } int main() { Scanner scanner; string s = scanner.get<string>(); int i = scanner.get<int>(); } The Scanner class is used to extract tokens from some source. The above code works fine, but fails when I try to get other integral types like a char or an unsigned int. The code to read these types is exactly the same as the code to read an int. I could just duplicate the code for all other integral types I'd like to read, but I'd rather define one function template for all integral types. I've tried the following: struct Scanner { template <typename T> typename enable_if<boost::is_integral<T>, T>::type get(); }; Which works like a charm, but I am unsure how to get Scanner::get<string>() to function again. So, how can I write code so that I can do scanner.get<string>() and scanner.get<any integral type>() and have a single definition to read all integral types? Update: bonus question: What if I want to accept more than one range of classes based on some traits? For example: how should I approach this problem if I want to have three get functions that accept (i) integral types (ii) floating point types (iii) strings, respectively.

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  • Execution issue with PyModule_AddIntConstant function

    - by karnol
    I m learning python c api functions and keen to learn python 3.1 stable version. Found an unresolved issue recently and tried PyModule_AddIntConstant(PyObject *module, const char *name, long value) Runtime error occurred for this function call. Is there something wrong with the function in python 3.1?

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  • Using "from __future__ import division" in my program, but it isn't loaded with my program

    - by Sara Fauzia
    I wrote the following program in Python 2 to do Newton's method computations for my math problem set, and while it works perfectly, for reasons unbeknownst to me, when I initially load it in ipython with %run -i NewtonsMethodMultivariate.py, the Python 3 division is not imported. I know this because after I load my Python program, entering x**(3/4) gives "1". After manually importing the new division, then x**(3/4) remains x**(3/4), as expected. Why is this? # coding: utf-8 from __future__ import division from sympy import symbols, Matrix, zeros x, y = symbols('x y') X = Matrix([[x],[y]]) tol = 1e-3 def roots(h,a): def F(s): return h.subs({x: s[0,0], y: s[1,0]}) def D(s): return h.jacobian(X).subs({x: s[0,0], y: s[1,0]}) if F(a) == zeros(2)[:,0]: return a else: while (F(a)).norm() > tol: a = a - ((D(a))**(-1))*F(a) print a.evalf(10) I would use Python 3 to avoid this issue, but my Linux distribution only ships SymPy for Python 2. Thanks to the help anyone can provide. Also, in case anyone was wondering, I haven't yet generalized this script for nxn Jacobians, and only had to deal with 2x2 in my problem set. Additionally, I'm slicing the 2x2 zero matrix instead of using the command zeros(2,1) because SymPy 0.7.1, installed on my machine, complains that "zeros() takes exactly one argument", though the wiki suggests otherwise. Maybe this command is only for the git version.

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  • catching erros and exiting

    - by apple pie
    In python, is there a way to exit a class after testing a condition, without exiting out of python? say i have the class class test(): def __init__(self): self.a = 2 def create_b(self): self.b = 3 def does_b_exist(self): if <self.b doesnt exist>: #terminate self.b += 1 try/except` doesnt work since the rest of the program doesnt terminate after failing. im basically trying to catch an error, and do what python does when it shows you errors, but i cant figure out how to do it

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  • Annotation based data structure visualization - are there similar tools out there?

    - by Helper Method
    For a project at university I plan to build an annotation based tool to visualize/play around with data structures. Here's my idea: Students which want to try out their self-written data structures need to: mark the type of their data structures using some sort of marker annotation e.g. @List public class MyList { ... } so that I know how to represent the data structure need to provide an iterator so that I can retrieve the elements in the right order need to annotate methods for insertion and removal, e.g. @add public boolean insert(E e) { ... } so that I can "bind" that method to some button. Do similar applications exist? I googled a little bit around but didn't find anything like that.

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  • ruby confusing -- local variable or instance_method ?

    - by boblu
    I have the following program. module C def self.included(base) base.extend(ClassMethods) end module ClassMethods def test_for class_eval <<-DEFINECLASSMETHODS def self.my_method(param_a) puts "SELF is: #{self.inspect}" puts param_a puts "#{param_a}" end DEFINECLASSMETHODS end end end class A include C end class B < A test_for end when I run B.new.my_method("aaa"), I got this error NameError: undefined local variable or method `param_a' for B:Class I am quite confused. I define param_a as a local variable in class method my_method, puts param_a runs good, and will output the "aaa". however, puts "#{param_a}" output that error. why? Can anyone explain this?

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  • Enumerate over an enum in C++

    - by jameszhao00
    In C++, Is it possible to enumerate over an enum (either runtime or compile time (preferred)) and call functions/generate code for each iteration? Sample use case: enum abc { start a, b, c, end } for each (__enum__member__ in abc) { function_call(__enum__member__); } Plausible duplicates: C++: Iterate through an enum Enum in C++ like Enum in Ada?

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  • Reason for unintuitive UnboundLocalError behaviour 2

    - by Jonathan
    Following up on Reason for unintuitive UnboundLocalError behaviour (I will assume you've read it). Consider the following Python script: def f(): # a+=1 # 1 aa=a aa+=1 # b+='b' # 2 bb=b bb+='b' c[0]+='c' # 3 c.append('c') cc=c cc.append('c') # 4 a=1 b='b' c=['c'] f() print a print b print c The result of the script is: 1 b ['cc', 'c', 'c'] The commented out lines (marked 1,2) are lines that would through an UnboundLocalError and the SO question I referenced explains why. However, the line marked 3 works! By default, lists are copied by reference in Python, therefore it's understandable that c changes when cc changes. But why should Python allow c to change in the first place, if it didn't allow changes to a and b directly from the method's scope? I don't see how the fact that by default lists are copied by reference in Python should make this design decision inconsistent. What am I missing folks?

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  • PyQt4 plugin in c++ application

    - by veverica17
    How is it posible to load python script as plugin in qt based application? The basic idea would be to make a class in c++ class b { virtual void method1(); virtual void method2(); } and 'somehow' inherit it in python like class c(b): def method1: #do something def method2: #do something I need to be able to modify the gui from python( add buttons to some widgets made in c++ with qt ). Basicaly something similiar to (gedit, blender, etc) plugin architecture with qt

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  • Disallow taking pointer/reference to const to a temporary object in C++ (no C++0X)

    - by KRao
    Hi, I am faced with the following issue. Consider the following class: //Will be similar to bost::reference_wrapper template<class T> class Ref { public: explicit Ref(T& t) : m_ptr(&t) {} private: T* m_ptr; }; and this function returning a double double fun() {return 1.0;} If we now have double x = 1.0; const double xc = 1.0; Ref<double> ref1(x); //OK Ref<const double> refc1(cx); //OK good so far, however: //Ref<double> ref2( fun() ); //Fails as I want it to Ref<const double> refc2( fun() ); //Works but I would like it not to Is there a way to modify Ref (the way you prefer) but not the function fun, so that the last line returns a compile-time error? Please notice you can modify the constructor signature (as long as I am able to initialise the Ref as intended). Thank you in advance for your help!

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  • specyfic syntax question

    - by bua
    Hi there, Is it possible to create template to the initialization like: template <typename C> typename C::value_type fooFunction(C& c) {...}; std::vector<string> vec_instance; fooFunction(cont<0>(vec_instance)); fooFunction(cont<1>(vec_instance)); In general i'm interested is it possible to specify template using integer (ie. 0) instead of true type name. And how to achieve above?

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