I couldn't find one looking at the API, but essentially I want the following: after all of the Visit* methods, I'd call a final method that does some postprocessing on my data members. I'd assume it'd be something similar to visiting a TranslationUnitDecl, except instead of being the first visit method, it'd be the last.
You can add do this within a HandleTranslationUnit method.
void MyVisitor::HandleTranslationUnit(ASTContext &Context) {
...
TraverseDecl(Context.getTranslationUnitDecl());
// Do post-processing here
}
Related
Developing a Drupal 8 example site, I have declared block in a module, and I want to do a few things with this block, like check the route and show this block only on nodes, also check if the user has permissions to see this block, and the content of the block is a form which I had defined in another place of the module.
I don't want to get the classes/services that I need in a static way, I want to use dependency injection to get those classes because it is technically better to decouple code and allow better testing.
Now "create" method and the "constructor" method on the block are like so:
<?php
public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition) {
return new static(
$configuration,
$plugin_id,
$plugin_definition,
$container->get('current_user'),
$container->get('form_builder'),
$container->get('current_route_match'),
$container->get('access_check.permission')
);
}
public function __construct(
array $configuration, $plugin_id,
$plugin_definition,
AccountProxyInterface $user,
FormBuilderInterface $formBuilder,
ResettableStackedRouteMatchInterface $route,
AccessInterface $access
) {
parent::__construct($configuration, $plugin_id, $plugin_definition);
$this->user = $user;
$this->formBuilder = $formBuilder;
$this->route = $route;
$this->access = $access;
}
Is this the correct way to do this? Maybe I'm doing too much in the block file? Should I create a service to move the logic to another place? Probably I would need more things, which means using more services, and my "create" and "constructor" methods are growing in parameters. Is this the correct way to do it? Thanks.
When you have to inject many services in one class, be it a controller or a block, it usually tells that the class is not well designed because you are (probably) trying lots of things in just one class.
However, I've seen many controllers which inject multiple services in their constructors, so it doesn't seem an unusual practice anyway. "Every rule has an exception".
In the end, I think it is a matter of balance, build a class that is responsible for doing one logical thing, and its dependencies in the same way.
Let me elaborate on the title:
I want to implement a system that would allow me to enable/disable/modify the general behavior of my program. Here are some examples:
I could switch off and on logging
I could change if my graphing program should use floating or pixel coordinates
I could change if my calculations should be based upon some method or some other method
I could enable/disable certain aspects like maybe a extension api
I could enable/disable some basic integrated profiler (if I had one)
These are some made-up examples.
Now I want to know what the most common solution for this sort of thing is.
I could imagine this working with some sort of singelton class that gets instanced globally or in some other globally available object. Another thing that would be possible would be just constexpr or other variables floating around in a namespace, again globally.
However doing something like that, globally, feels like bad practise.
second part of the question
This might sound like I cant decide what I want, but I want a way to modify all these switches/flags or whatever they are actually called in a single location, without tying any of my classes to it. I don't know if this is possible however.
Why don't I want to do that? Well I like to make my classes somewhat reusable and I don't like tying classes together, unless its required by the DRY principle and or inheritance. I basically couldn't get rid of the flags without modifying the possible hundreds of classes that used them.
What I have tried in the past
Having it all as compiler defines. This worked reasonably well, however I didnt like that I couldnt make it so if the flag file was gone there were some sort of default settings that would make the classes themselves still operational and changeable (through these default values)
Having it as a class and instancing it globally (system class). Worked ok, however I didnt like instancing anything globally. Also same problem as above
Instancing the system class locally and passing it to the classes on construction. This was kinda cool, since I could make multiple instruction sets. However at the same time that kinda ruined the point since it would lead to things that needed to have one flag set the same to have them set differently and therefore failing to properly work together. Also passing it on every construction was a pain.
A static class. This one worked ok for the longest time, however there is still the problem when there are missing dependencies.
Summary
Basically I am looking for a way to have a single "place" where I can mess with some values (bools, floats etc.) and that will change the behaviour of all classes using them for whatever, where said values either overwrite default values or get replaced by default values if said "place" isnt defined.
If a Singleton class does not work for you , maybe using a DI container may fit in your third approach? It may help with the construction and make the code more testable.
There are some DI frameworks for c++, like https://github.com/google/fruit/wiki or https://github.com/boost-experimental/di which you can use.
If you decide to use switch/flags, pay attention for "cyclometric complexity".
If you do not change the skeleton of your algorithm but only his behaviour according to the objets in parameter, have a look at "template design pattern". This method allow you to define a generic algorithm and specify particular step for a particular situation.
Here's an approach I found useful; I don't know if it's what you're looking for, but maybe it will give you some ideas.
First, I created a BehaviorFlags.h file that declares the following function:
// Returns true iff the given feature/behavior flag was specified for us to use
bool IsBehaviorFlagEnabled(const char * flagName);
The idea being that any code in any of your classes could call this function to find out if a particular behavior should be enabled or not. For example, you might put this code at the top of your ExtensionsAPI.cpp file:
#include "BehaviorFlags.h"
static const enableExtensionAPI = IsBehaviorFlagEnabled("enable_extensions_api");
[...]
void DoTheExtensionsAPIStuff()
{
if (enableExtensionsAPI == false) return;
[... otherwise do the extensions API stuff ...]
}
Note that the IsBehaviorFlagEnabled() call is only executed once at program startup, for best run-time efficiency; but you also have the option of calling IsBehaviorFlagEnabled() on every call to DoTheExtensionsAPIStuff(), if run-time efficiency is less important that being able to change your program's behavior without having to restart your program.
As far as how the IsBehaviorFlagEnabled() function itself is implemented, it looks something like this (simplified version for demonstration purposes):
bool IsBehaviorFlagEnabled(const char * fileName)
{
// Note: a real implementation would find the user's home directory
// using the proper API and not just rely on ~ to expand to the home-dir path
std::string filePath = "~/MyProgram_Settings/";
filePath += fileName;
FILE * fpIn = fopen(filePath.c_str(), "r"); // i.e. does the file exist?
bool ret = (fpIn != NULL);
fclose(fpIn);
return ret;
}
The idea being that if you want to change your program's behavior, you can do so by creating a file (or folder) in the ~/MyProgram_Settings directory with the appropriate name. E.g. if you want to enable your Extensions API, you could just do a
touch ~/MyProgram_Settings/enable_extensions_api
... and then re-start your program, and now IsBehaviorFlagEnabled("enable_extensions_api") returns true and so your Extensions API is enabled.
The benefits I see of doing it this way (as opposed to parsing a .ini file at startup or something like that) are:
There's no need to modify any "central header file" or "registry file" every time you add a new behavior-flag.
You don't have to put a ParseINIFile() function at the top of main() in order for your flags-functionality to work correctly.
You don't have to use a text editor or memorize a .ini syntax to change the program's behavior
In a pinch (e.g. no shell access) you can create/remove settings simply using the "New Folder" and "Delete" functionality of the desktop's window manager.
The settings are persistent across runs of the program (i.e. no need to specify the same command line arguments every time)
The settings are persistent across reboots of the computer
The flags can be easily modified by a script (via e.g. touch ~/MyProgram_Settings/blah or rm -f ~/MyProgram_Settings/blah) -- much easier than getting a shell script to correctly modify a .ini file
If you have code in multiple different .cpp files that needs to be controlled by the same flag-file, you can just call IsBehaviorFlagEnabled("that_file") from each of them; no need to have every call site refer to the same global boolean variable if you don't want them to.
Extra credit: If you're using a bug-tracker and therefore have bug/feature ticket numbers assigned to various issues, you can creep the elegance a little bit further by also adding a class like this one:
/** This class encapsulates a feature that can be selectively disabled/enabled by putting an
* "enable_behavior_xxxx" or "disable_behavior_xxxx" file into the ~/MyProgram_Settings folder.
*/
class ConditionalBehavior
{
public:
/** Constructor.
* #param bugNumber Bug-Tracker ID number associated with this bug/feature.
* #param defaultState If true, this beheavior will be enabled by default (i.e. if no corresponding
* file exists in ~/MyProgram_Settings). If false, it will be disabled by default.
* #param switchAtVersion If specified, this feature's default-enabled state will be inverted if
* GetMyProgramVersion() returns any version number greater than this.
*/
ConditionalBehavior(int bugNumber, bool defaultState, int switchAtVersion = -1)
{
if ((switchAtVersion >= 0)&&(GetMyProgramVersion() >= switchAtVersion)) _enabled = !_enabled;
std::string fn = defaultState ? "disable" : "enable";
fn += "_behavior_";
fn += to_string(bugNumber);
if ((IsBehaviorFlagEnabled(fn))
||(IsBehaviorFlagEnabled("enable_everything")))
{
_enabled = !_enabled;
printf("Note: %s Behavior #%i\n", _enabled?"Enabling":"Disabling", bugNumber);
}
}
/** Returns true iff this feature should be enabled. */
bool IsEnabled() const {return _enabled;}
private:
bool _enabled;
};
Then, in your ExtensionsAPI.cpp file, you might have something like this:
// Extensions API feature is tracker #4321; disabled by default for now
// but you can try it out via "touch ~/MyProgram_Settings/enable_feature_4321"
static const ConditionalBehavior _feature4321(4321, false);
// Also tracker #4222 is now enabled-by-default, but you can disable
// it manually via "touch ~/MyProgram_Settings/disable_feature_4222"
static const ConditionalBehavior _feature4222(4222, true);
[...]
void DoTheExtensionsAPIStuff()
{
if (_feature4321.IsEnabled() == false) return;
[... otherwise do the extensions API stuff ...]
}
... or if you know that you are planning to make your Extensions API enabled-by-default starting with version 4500 of your program, you can set it so that Extensions API will be enabled-by-default only if GetMyProgramVersion() returns 4500 or greater:
static ConditionalBehavior _feature4321(4321, false, 4500);
[...]
... also, if you wanted to get more elaborate, the API could be extended so that IsBehaviorFlagEnabled() can optionally return a string to the caller containing the contents of the file it found (if any), so that you could do shell commands like:
echo "opengl" > ~/MyProgram_Settings/graphics_renderer
... to tell your program to use OpenGL for its 3D graphics, or etc:
// In Renderer.cpp
std::string rendererType;
if (IsDebugFlagEnabled("graphics_renderer", &rendererType))
{
printf("The user wants me to use [%s] for rendering 3D graphics!\n", rendererType.c_str());
}
else printf("The user didn't specify what renderer to use.\n");
I need to apply a lot of functions to the same piece of data in arbitrary order. Different people add different functions. I have created a system, that, after simplification, looks like that:
abstract_filter.h
class AbstractFilter {
void filter(data) = 0;
}
blue_filter.h
class BlueFilter: public AbstractFilter ...
red_filter.h ...
green_filter.h ...
parser.cpp
#include "blue_filter.h"
#include "red_filter.h" //so on
void Parse(const Data data) {
RedFilter redFilter();
redFilter.filter(data);
BlueFilter blueFilter();
blueFilter.filter(data);
....
}
I have hundreds of filters and people always forget to add them to the list or configure. Is it possible to write something like "take all classes from that group/folder and instantiate and put in array...."? I can't make them static or register filters in their constructors because several filtering stacks can be active in the same time.
All I want is to not have to manually enumerate all filters. Would be great to put them in place by just adding them to the project.
Write a python script which parses the filter directory entries an adds them to a generic factory or processing class. If the script runs on every build process the filters will always be taken care of.
This is a fairly straight forward question but I am unable to find an answer about this specific type of formatting. I'm looking for a way to modify where eclipse places the cursor after using its content assist to complete a method call based on whether or not the method has any parameters.
To illustrate what exactly I'm talking about lets consider a simple c++ class like so:
class Example
{
public:
int voidParams()
{
//do something
return 42;
};
int nonVoidParams(int a)
{
//do something else
return a*a;
};
};
And at some point I created an instance of the class Example ex;
Now within eclipse if I started typing ex.nonV and I told eclipse to auto complete it would enter in ex.nonVoidParams() and after doing this my cursor would be inside the parenthesis like so ex.nonVoidParams(|) where | is my cursor. This makes sense and is useful since I need to give this particular method an argument.
Hopefully none of what I just said is new to anyone and is all pretty straight forward. This is where my question comes in. Having my cursor be placed within the parenthesis of a method call is only useful if that method takes parameters. If I were to type ex.voi and let eclipse auto complete to ex.voidParams() my cursor would be inside the parenthesis like so ex.voidParams(|) where | is my cursor. This isn't very useful since there is nothing for me to enter there.
I would like to know if there is a way to setup eclipse so, given the above examples, if it auto completes a method with void parameters such as ex.voidParams() it places the cursor after the method call like so ex.voidParams()| again where | is my cursor.
I'm not super familiar with customizing eclipse but I feel like there should be a way to do this since if eclipse is auto completing the method call it should know what its parameters are and be able to adjust its formatting from there.
Oh and this will probably be asked at some point, I'm currently using Eclipse CDT version 4.2.0 (Juno service Release 2).
Go to Window->Preferences->C++->Editor->Content Assist->Advanced, pick the "Parsing-based Proposals" instead of "Parsing-based Proposals (Task-Focused)".
I have created a pass that pathprofiles and then stores results in different data structures such as blocks corresponding to the paths, edges in paths etc.
I have different variables and data structures for each of these.
Is there a way to use these variables directly in another pass that i write?
If yes, how? (Im not sure if getAnalysisUsage works for this?)
Urgent help required
This answer might be late, but I had the same question, ran across your post and thanks to Oak was pointed into the right direction. So I wanted to share some code here.
Suppose you have two passes, the first one is your PathProfilePass and the second one is your DoSomethingPass. The first pass contains the data that you collect and share with the second path; nothing special needs to be done here:
/// Path profiling to gather heaps of data.
class PathProfilePass: public llvm::ModulePass {
public:
virtual bool runOnModule(llvm::Module &M) {
// Create goodness for edges and paths.
...
}
std::set<Edges> edges; ///< All the edges this pass collects.
std::set<Paths> paths; ///< All the paths this pass collects.
};
The interesting stuff happens in the second pass. Two things you need to do here:
Specify the dependency of the second pass on the first pass: see the getAnalysisUsage method.
Access the data from the first pass: see the getAnalysis method.
Code-wise it would look something like this for the second pass:
/// Doing something with edge and path informations.
class DoSomethingPass: public llvm::ModulePass {
public:
/// Specify the dependency of this pass on PathProfilePass.
virtual void getAnalysisUsage(llvm::AnalysisUsage &AU) const {
AU.addRequired<PathProfilePass>();
}
/// Use the data of the PathProfilePass.
virtual bool runOnModule(llvm::Module &M) {
PathProfilePass &PPP = getAnalysis<PathProfilePass>();
// Get the edges and paths from the first pass.
std::set<Edges> &edges = PPP.edges;
std::set<Paths> &paths = PPP.paths;
// Now you can noodle over that data.
...
}
};
Disclaimer: I haven't compiled this code, but this is an adaptation to your example of what works for me. Hope this is useful :-)
Set a dependency from the 2nd pass to the 1st pass (via overriding getAnalysisUsage and invoking getAnalysis - see the programmer's guide to writing a pass on how to do that). Once you get an instance of the 1st pass, you can use it just like any other C++ object.