I'm using Calcite for parsing and executing queries, and can't figure out how to implement functions like Postgres' current_schema(). For functions with non-reserved keywords, ex: VERSION(), the implementation is fairly straightforward:
private void addRootOperators() {
SchemaPlus plus = this.rootSchema.plus();
// VersionFunction is a custom class with a run() method
plus.add("VERSION", ScalarFunctionImpl.create(VersionFunction.class, "run"));
}
Unfortunately this approach doesn't work when I try to implement CURRENT_SCHEMA(), though it will if I give it a non-reserved name.
When I run the query SELECT current_schema() with the function defined like VERSION above, I get the error:
Encountered "(" at line 1, column 22
I believe this is because the default implementation of CURRENT_SCHEMA is as a SqlStringContextVariable (hence why the parentheses are causing a parsing error), but I don't know how to support the version of the function with the parentheses in light of this.
Related
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 have a feeling this is a bug in CF9, from looking at this: How to specify argument attributes in CFscript? (CF9)
However, if not, I'm writing a cfscript component in CF9 (pure), and attempting to pass an argument as a type of user defined cfc.
public function init(required _lbr._core._sharing._access.accessLinkDAO oAccessLinkDAO) returntype="_lbr._core._sharing._access.accessLinkBusiness" {
But CF keeps coming back with:
You cannot use a variable reference with "." operators in this context
is this something broken with CF9 pure?
I have confirmed this is a bug in CF9.0 (and fixed in one of CF9.0.1 or CF9.0.2; probably 9.0.1).
However the fix is easy. The problem is only with the dotted paths, and as #ScottStroz points out, you don't need them. This works fine:
component {
public accessLinkBusiness function init(required accessLinkDAO oAccessLinkDAO) {
return this;
}
}
I've moved the return type simply because that's just the normal place for it: it'll work as attribute too (but that syntax is just awful).
If the CFCs you are referencing as return types or argument types aren't in the same dir as the CFC using them, use an import statement, eg in this case:
import _lbr._core._sharing._access.*;
I have one file "example.lua":
local function manipulate(something)
return string.rep(something, 3) -- repeats the given string
end
function apiFunction(somethingelse)
return manipulate(somethingelse)
end
and another files (main.lua) task is to "load"/"do" it:
loadAPI("example.lua", "externAPI") --< the part i need help with
externAPI.apiFunction("Test") --> should return TestTestTest
the thing that should happen is, that example.lua gets executed just like
dofile("example.lua")
but everything globally "defined" within example.lua (in this case the apiFunction) moves to the new generated global "externAPI" table and the rest (ie. manipulate) is hidden and only available from inside the example.lua file.
I've seen this bahaviour before in the minecraft mod "ComputerCraft" in which there is a function called "os.loadAPI("/somepath/sha-2") and it would define the definitions in the sha-2-chunk in the due to the name specified "sha-2"-table.
I've been searching for this sort of scoping/redirecting stuff for a while but there are no solutions putting the stuff into the new table.
I've been thinking of parsing the _G table after new indexes and move those to the new table but I'm sure there are some lua-magicians out here that know a much cleaner, better working solution to this.
All this is in one C lua_state* , so if there are any solutions adding this loadAPI function in C/C++ and just registrating it at the state this would be fine, too.
I've also looked at "require", but didn't seem to understand whether it does what I need.
Using Lua 5.2.3
Hope i didn't forget anything.
Thanks in advance :)
~InDieTasten
Try this:
function loadAPI(f,g)
_G[g]=setmetatable({},{__index=_G})
loadfile(f,"bt",_G[g])()
end
loadAPI("example.lua", "externAPI")
print(externAPI.apiFunction("Test"))
I'm trying to use the Code Templates feature with PHP in NetBeans (7.3), however I'm finding it rather limited. Given the following desired output:
public function addFoo(Foo $foo) {
$this->fooCollection[] = $foo;
}
I'm trying to have every instance of "foo"/"Foo" be variable; so I used a variable:
public function add${name}(${name} $$${name}) {
$this->${name}Collection[] = $$${name};
}
Of course, when expanded there isn't any regard given to the desired capitalization rules, because I can't find a way to implement that; the result being (given I populate ${name} with "Foo"):
public function addFoo(Foo $Foo) { // note the uppercase "Foo" in the argument
$this->FooCollection[] = $Foo; // and collection property names...
} // not what I had in mind
Now, I've read that NetBeans supports FreeMarker in it's templates, but that seems to be only for file-templates and not snippet-templates like these.
As far as I can tell, the FreeMarker version would look something like the following; however, it doesn't work, and ${name?capitalize} is simply seen as another variable name.
public function add${name?capitalize}(${name?capitalize} $$${name}) {
$this->${name}Collection[] = $$${name};
}
Passing "foo", allowing capitalize to fix it for type-names, second-words, etc.
Is there any way to get FreeMarker support here, or an alternative?
I'm open to any suggestions really; third-party plugins included. I just don't want to have to abandon NetBeans.
Addendum
The example given is trivial; an obvious solution for it specifically would be:
public function add${upperName}(${upperName} $$${lowerName}) {
$this->${lowerName}Collection[] = $$${lowerName};
}
Where upper/lower would be "Foo"/"foo" respectively. However, it's just an example, and I'm looking for something more robust in general (such as FreeMarker support)
I think this would increase the quality of life when devving, but google came up with nothing and I couldn't find anything specific inside inside Netbeans either.
What I want is to start with this header:
class bla
{
public:
static void gfg(somearg asd);
};
Then I open the blank bla.cpp and pressed 'autoimplement'. After that, it would look like this:
#include "bla.h"
static void bla::gfg(somearg asd)
{
//TODO: implement
throw unimplemented("void bla::gfg(somearg) is unimplemented");
}
Anyone know of a tool like this?
I found http://www.radwin.org/michael/projects/stubgen/
"stubgen is a C++ development tool that keeps code files in sync with their associated headers. When it finds a member function declaration in a header file that doesn't have a corresponding implementation, it creates an empty skeleton with descriptive comment headers."
This looks like it does exactly what you want it to do.
Some time has passed and in the meantime the requested feature seems to have been implemented in netbeans. Refer to https://netbeans.org/bugzilla/show_bug.cgi?id=213811 , which also gives a description on how to use it:
Note:
Implemented CTRL+SPACE.
IDE suggest implementing of class method if CTRL+SPACE was pressed:
- inside file that already has at least one method definition
- between method declarations