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I started a new Kotlin project and i want to use the arrow-kt core Lib in combination with Quarkus (1.12.2). I want to use the native compilation feature of Quarkus with the GraalVM. My first thought was that arrow is a simple lib without reflection but then i read that.
Since GraalVm has a problem with reflection in native executables at runtime, will that be a problem with Arrow? If it is a problem, can i bypass the problem by simply avoiding some features of Arrow?
I know that i can mark classes for reflection in Quarkus/GraalVM.
Which classes are inspected by reflection? Can i simply add reflection information for a few classes or do i need to that for the whole lib or my whole code?
Starting in 0.12.0, which is about to release, Arrow does not use reflection. Previously it did in monad comprehensions for all inheritors of MonadContinuation in their bind operation accessing the ContinuationUtils class. In this class, we used reflection to read and write private fields related to the continuation stack labels.
As another answer states a newer release might not use reflection, making the question about the particular library not that important. However, for completeness, here are some answers to these questions in general.
Since GraalVm has a problem with reflection in native executables at
runtime, will that be a problem with Arrow?
GraalVM native image uses static analysis during building the executable out of your program. This means that dynamic features of the langauge require explicit configuration to help the analysis to include the necessary classes / methods into the binary. For example, static analysis cannot predict which classes will be accessed through reflection or proxied when these are referenced through strings only which can sometimes are constructed only at runtime.
Can i simply add reflection information for a few classes or do i need to that for the whole lib or my whole code?
You do need to configure all the accesses through the reflection API. The libraries can provide the config for their use of reflection, resources, etc. But if they need refletive access to your application classes then they cannot do that.
The configuration required is in the form of json files, for example a reflection configuration to include a class might look like:
[
{
"name" : "java.lang.String",
"fields" : [
{ "name" : "value", "allowWrite" : true },
{ "name" : "hash" }
],
"methods" : [
{ "name" : "<init>", "parameterTypes" : [] },
{ "name" : "<init>", "parameterTypes" : ["char[]"] },
{ "name" : "charAt" },
{ "name" : "format", "parameterTypes" : ["java.lang.String", "java.lang.Object[]"] }
]
}
]
The example above specifies that the program would like to be able to use java.lang.String reflectively, have access to the fields value and hash and the methods listed.
It might be a bit tedious, however rather straightforward to create config like that. Some frameworks help you by providing annotations to mark classes with and then generate the config themselves.
But if you want to create the config for the library that you don't know, so it's hard to manually create the config, you can use and it's recommended to use the assisted configuration agent.
This means you execute your program enabling a javaagent, which will trace and write down config for all necessary features: resource access, serialization/deserialization, proxies, JNI, reflection, etc.
So you run the application like this and execute the codepaths you're interested in (maybe through your tests) and the output dir will contain the config.
java -agentlib:native-image-agent=config-output-dir=/path/to/config-dir/ -jar myjar.jar
You can then edit the config if needed manually to, for example, extrapolate to the code paths you didn't run with the tracing agent.
Then you run the native image build process passing the config options, for example, for the reflection file config specify:
-H:ReflectionConfigurationFiles=/path/to/reflectconfig.
You can also use the fact that META-INF/native-image directory is the default location for the configuration files, so you don't have to specify the options. For example if you generate the config in the config/META-INF/native-image directory, then you can place it on the classpath for the native image and the files will be picked up automatically:
native-image -cp config -jar myjar.jar
I prefer working with files that are less than 1000 lines long, so am thinking of breaking up some Erlang modules into more bite-sized pieces.
Is there a way of doing this without expanding the public API of my library?
What I mean is, any time there is a module, any user can do module:func_exported_from_the_module. The only way to really have something be private that I know of is to not export it from any module (and even then holes can be poked).
So if there is technically no way to accomplish what I'm looking for, is there a convention?
For example, there are no private methods in Python classes, but the convention is to use a leading _ in _my_private_method to mark it as private.
I accept that the answer may be, "no, you must have 4K LOC files."
The closest thing to a convention is to use edoc tags, like #private and #hidden.
From the docs:
#hidden
Marks the function so that it will not appear in the
documentation (even if "private" documentation is generated). Useful
for debug/test functions, etc. The content can be used as a comment;
it is ignored by EDoc.
#private
Marks the function as private (i.e., not part of the public
interface), so that it will not appear in the normal documentation.
(If "private" documentation is generated, the function will be
included.) Only useful for exported functions, e.g. entry points for
spawn. (Non-exported functions are always "private".) The content can
be used as a comment; it is ignored by EDoc.
Please note that this answer started as a comment to #legoscia's answer
Different visibilities for different methods is not currently supported.
The current convention, if you want to call it that way, is to have one (or several) 'facade' my_lib.erl module(s) that export the public API of your library/application. Calling any internal module of the library is playing with fire and should be avoided (call them at your own risk).
There are some very nice features in the BEAM VM that rely on being able to call exported functions from any module, such as
Callbacks (funs/anonymous funs), MFA, erlang:apply/3: The calling code does not need to know anything about the library, just that it's something that needs to be called
Behaviours such as gen_server need the previous point to work
Hot reloading: You can upgrade the bytecode of any module without stopping the VM. The code server inside the VM maintains at most two versions of the bytecode for any module, redirecting external calls (those with the Module:) to the most recent version and the internal calls to the current version. That's why you may see some ?MODULE: calls in long-running servers, to be able to upgrade the code
You'd be able to argue that these points'd be available with more fine-grained BEAM-oriented visibility levels, true. But I don't think it would solve anything that's not solved with the facade modules, and it'd complicate other parts of the VM/code a great deal.
Bonus
Something similar applies to records and opaque types, records only exist at compile time, and opaque types only at dialyzer time. Nothing stops you from accessing their internals anywhere, but you'll only find problems if you go that way:
You insert a new field in the record, suddenly, all your {record_name,...} = break
You use a library that returns an opaque_adt(), you know that it's a list and use like so. The library is upgraded to include the size of the list, so now opaque_adt() is a tuple() and chaos ensues
Only those functions that are specified in the -export attribute are visible to other modules i.e "public" functions. All other functions are private. If you have specified -compile(export_all) only then all functions in module are visible outside. It is not recommended to use -compile(export_all).
I don't know of any existing convention for Erlang, but why not adopt the Python convention? Let's say that "library-private" functions are prefixed with an underscore. You'll need to quote function names with single quotes for that to work:
-module(bar).
-export(['_my_private_function'/0]).
'_my_private_function'() ->
foo.
Then you can call it as:
> bar:'_my_private_function'().
foo
To me, that communicates clearly that I shouldn't be calling that function unless I know what I'm doing. (and probably not even then)
The official site of Typescript get me ask a question,
"Do we need to use namespace or not?".
The following quote explains the 2 things well:
It’s important to note that in TypeScript 1.5, the nomenclature has
changed. “Internal modules” are now “namespaces”. “External modules”
are now simply “modules”, as to align with ECMAScript 2015’s
terminology, (namely that module X { is equivalent to the
now-preferred namespace X {).
So, they suggest that TS team prefer namespace.
Further, it says we should use "namespace" to struct the internal module:
This post outlines the various ways to organize your code using
namespaces (previously “internal modules”) in TypeScript. As we
alluded in our note about terminology, “internal modules” are now
referred to as “namespaces”. Additionally, anywhere the module keyword
was used when declaring an internal module, the namespace keyword can
and should be used instead. This avoids confusing new users by
overloading them with similarly named terms.
The above quote is all from the Namespace section, and yes, it says again, but in a internal secnario.
but in the module section, one paragraph, says that:
Starting with ECMAScript 2015, modules are native part of the
language, and should be supported by all compliant engine
implementations. Thus, for new projects modules would be the
recommended code organization mechanism.
Does it mean that I don't need to bother with namespace, use module all along is the suggested way to develop?
Does it mean that I don't need to bother with namespace, use module all along is the suggested way to develop?
I wouldn't put it exactly that way... here's another paraphrase of what has happened. One upon a time, there were two terms used in Typescript
"external modules" - this was the TS analog to what the JS community called AMD (e.g. RequireJS) or CommonJS (e.g. NodeJS) modules. This was optional, for some people who write browser-based code only, they don't always bother with this, especially if they use globals to communicate across files.
"internal modules" - this is a hierarchical way of organising your variables/functions so that not everything is global. The same pattern exists in JS, it's when people organise their variables into objects/nested objects rather than having them all global.
Along came Ecmascript 2015 (a.k.a. ES6), which added a new formal, standard format that belonged in the "external modules" category. Because of this change, Typescript wanted to change the terminology to match the new Javascript standard (being that it likes to be a superset of Javascript, and tries its best to avoid confusion for users coming from Javascript). Thus, the switch of "external modules" being simplified to just "modules", and "internal modules" being renamed to "namespaces".
The quote you found here:
Starting with ECMAScript 2015, modules are native part of the language, and should be supported by all compliant engine implementations. Thus, for new projects modules would be the recommended code organization mechanism.
Is likely alluding to guidance for users who were not yet using (external) modules. To at least consider using it now. However, support for ES6 modules is still incomplete in that browsers as of May 2016 don't have built-in module loaders. So, you either have to add a polyfill (which handles it at runtime) like RequireJS or SystemJS, or a bundler (like browserify or webpack) that handles it at build time (before you deploy to your website).
So, would you ever use both modules (formerly "external modules") and namespaces? Absolutely - I use them both frequently in my codebases. I use (external) modules to organise my code files.
Namespaces in Typescript are extremely useful. Specifically, I use namespace declaration merging as a typesafe way to add extra properties to function objects themselves (a pattern often used in JS). In addition, while namespaces are a lot like regular object variables, you can hang subtypes (nested interfaces, classes, enums, etc.) off of their names.
Here is an example of a function with a property (very common in NodeJS libs):
function someUsefulFunction() {
// asynchronous version
return ...; // some promise
}
namespace someUsefulFunction {
export function sync() {
// synchronous version
}
}
This allows for consumers to do this common NodeJS pattern:
// asynchronous consumer
someUsefulFunction()
.then(() => {
// ...
});
// synchronous consumer
someUsefulFunction.sync();
Similarly, say you have an API that takes in an options object. If that options type is specific to that API,
function myFunc(options?: myFunc.Options) {
// ...
}
namespace myFunc {
export interface Options {
opt1?: number;
opt2?: boolean;
opt3?: string;
}
}
In that case, you don't have to pollute a larger namespace (say whole module scope) with the type declaration for the options.
Hope this helps!
I understand that the module! type provides a better structure for protected namespaces than object! or the 'use function. How are words bound within the module—I notice some errors related to unbound words:
REBOL [Type: 'module] set 'foo "Bar"
Also, how does Rebol distinguish between a word local to the module ('foo) and that of a system function ('set)?
Minor update, shortly after:
I see there's a switch that changes the method of binding:
REBOL [Type: 'module Options: [isolate]] set 'foo "Bar"
What does this do differently? What gotchas are there in using this method by default?
OK, this is going to be a little tricky.
In Rebol 3 there are no such things as system words, there are just words. Some words have been added to the runtime library lib, and set is one of those words, which happens to have a function assigned to it. Modules import words from lib, though what "import" means depends on the module options. That might be more tricky than you were expecting, so let me explain.
Regular Modules
For starters, I'll go over what importing means for "regular" modules, ones that don't have any options specified. Let's start with your first module:
REBOL [Type: 'module] set 'foo "Bar"
First of all, you have a wrong assumption here: The word foo is not local to the module, it's just the same as set. If you want to define foo as a local word you have to use the same method as you do with objects, use the word as a set-word at the top level, like this:
REBOL [Type: 'module] foo: "Bar"
The only difference between foo and set is that you hadn't exported or added the word foo to lib yet. When you reference words in a module that you haven't declared as local words, it has to get their values and/or bindings from somewhere. For regular modules, it binds the code to lib first, then overrides that by binding the code again to the module's local context. Any words defined in the local context will be bound to it. Any words not defined in the local context will retain their old bindings, in this case to lib. That is what "importing" means for regular modules.
In your first example, assuming that you haven't done so yourself, the word foo was not added to the runtime library ahead of time. That means that foo wasn't bound to lib, and since it wasn't declared as a local word it wasn't bound to the local context either. So as a result, foo wasn't bound to anything at all. In your code that was an error, but in other code it might not be.
Isolated Modules
There is an "isolate" option that changes the way that modules import stuff, making it an "isolated" module. Let's use your second example here:
REBOL [Type: 'module Options: [isolate]] set 'foo "Bar"
When an isolated module is made, every word in the module, even in nested code, is collected into the module's local context. In this case, it means that set and foo are local words. The initial values of those words are set to whatever values they have in lib at the time the module is created. That is, if the words are defined in lib at all. If the words don't have values in lib, they won't initially have values in the module either.
It is important to note that this import of values is a one-time thing. After that initial import, any changes to these words made outside the module don't affect the words in the module. That is why we say the module is "isolated". In the case of your code example, it means that someone could change lib/set and it wouldn't affect your code.
But there's another important module type you missed...
Scripts
In Rebol 3, scripts are another kind of module. Here's your code as a script:
REBOL [] set 'foo "Bar"
Or if you like, since script headers are optional in Rebol 3:
set 'foo "Bar"
Scripts also import their words from lib, and they import them into an isolated context, but with a twist: All scripts share the same isolated context, known as the "user" context. This means that when you change the value of a word in a script, the next script to use that word will see the change when it starts. So if after running the above script, you try to run this one:
print foo
Then it will print "Bar", rather than have foo be undefined, even though foo is still not defined in lib. You might find it interesting to know that if you are using Rebol 3 interactively, entering commands into the console and getting results, that every command line you enter is a separate script. So if your session looks like this:
>> x: 1
== 1
>> print x
1
The x: 1 and print x lines are separate scripts, the second taking advantage of the changes made to the user context by the first.
The user context is actually supposed to be task-local, but for the moment let's ignore that.
Why the difference?
Here is where we get back to the "system function" thing, and that Rebol doesn't have them. The set function is just like any other function. It might be implemented differently, but it's still a normal value assigned to a normal word. An application will have to manage a lot of these words, so that's why we have modules and the runtime library.
In an application there will be stuff that needs to change, and other stuff that needs to not change, and which stuff is which depends on the application. You will want to group your stuff, to keep things organized or for access control. There will be globally defined stuff, and locally defined stuff, and you will want to have an organized way to get the global stuff to the local places, and vice-versa, and resolve any conflicts when more than one thing wants to define stuff with the same name.
In Rebol 3, we use modules to group stuff, for convenience and access control. We use the runtime library lib as a place to collect the exports of the modules, and resolve conflicts, in order to control what gets imported to the local places like other modules and the user context(s). If you need to override some stuff, you do this by changing the runtime library, and if necessary propagating your changes out to the user context(s). You can even upgrade modules at runtime, and have the new version of the module override the words exported by the old version.
For regular modules, when things are overridden or upgraded, your module will benefit from such changes. Assuming those changes are a benefit, this can be a good thing. A regular module cooperates with other regular modules and scripts to make a shared environment to work in.
However, sometimes you need to stay separate from these kinds of changes. Perhaps you need a particular version of some function and don't want to be upgraded. Perhaps your module will be loaded in a less trustworthy environment and you don't want your code hacked. Perhaps you just need things to be more predictable. In cases like this, you may want to isolate your module from these kinds of external changes.
The downside to being isolated is that, if there are changes to the runtime library that you might want, you're not going to get them. If your module is somehow accessible (such as by having been imported with a name), someone might be able to propagate those changes to you, but if you're not accessible then you're out of luck. Hopefully you've thought to monitor lib for changes you want, or reference the stuff through lib directly.
Still, we've missed another important issue...
Exporting
The other part of managing the runtime library and all of these local contexts is exporting. You have to get your stuff out there somehow. And the most important factor is something that you wouldn't suspect: whether or not your module has a name.
Names are optional for Rebol 3's modules. At first this might seem like just a way to make it simpler to write modules (and in Carl's original proposal, that is exactly why). However, it turns out that there is a lot of stuff that you can do when you have a name that you can't when you don't, simply because of what a name is: a way to refer to something. If you don't have a name, you don't have a way to refer to something.
It might seem like a trivial thing, but here are some things that a name lets you do:
You can tell whether a module is loaded.
You can make sure a module is only loaded once.
You can tell whether an older version of a module was there earlier, and maybe upgrade it.
You can get access to a module that was loaded earlier.
When Carl decided to make names optional, he gave us a situation where it would be possible to make modules for which you couldn't do any of those things. Given that module exports were intended to be collected and organized in the runtime library, we had a situation where you could have effects on the library that you couldn't easily detect, and modules that got reloaded every time they were imported.
So for safety we decided to cut out the runtime library completely and just export words from these unnamed modules directly to the local (module or user) contexts that were importing them. This makes these modules effectively private, as if they are owned by the target contexts. We took a potentially awkward situation and made it a feature.
It was such a feature that we decided to support it explicitly with a private option. Making this an explicit option helps us deal with the last problem not having a name caused us: making private modules not have to reload over and over again. If you give a module a name, its exports can still be private, but it only needs one copy of what it's exporting.
However, named or not, private or not, that is 3 export types.
Regular Named Modules
Let's take this module:
REBOL [type: module name: foo] export bar: 1
Importing this adds a module to the loaded modules list, with the default version of 0.0.0, and exports one word bar to the runtime library. "Exporting" in this case means adding a word bar to the runtime library if it isn't there, and setting that word lib/bar to the value that the word foo/bar has after foo has finished executing (if it isn't set already).
It is worth noting that this automatic exporting happens only once, when the body of foo is finished executing. If you make a change to foo/bar after that, that doesn't affect lib/bar. If you want to change lib/bar too, you have to do it manually.
It is also worth noting that if lib/bar already exists before foo is imported, you won't have another word added. And if lib/bar is already set to a value (not unset), importing foo won't overwrite the existing value. First come, first served. If you want to override an existing value of lib/bar, you'll have to do so manually. This is how we use lib to manage overrides.
The main advantages that the runtime library gives us is that we can manage all of our exported words in one place, resolving conflicts and overrides. However, another advantage is that most modules and scripts don't actually have to say what they are importing. As long as the runtime library is filled in properly ahead of time with all the words you need, your script or module that you load later will be fine. This makes it easy to put a bunch of import statements and any overrides in your startup code which sets up everything the rest of your code will need. This is intended to make it easier to organize and write your application code.
Named Private Modules
In some cases, you don't want to export your stuff to the main runtime library. Stuff in lib gets imported into everything, so you should only export stuff to lib that you want to make generally available. Sometimes you want to make modules that only export stuff for the contexts that want it. Sometimes you have some related modules, a general facility and a utility module or so. If this is the case, you might want to make a private module.
Let's take this module:
REBOL [type: module name: foo options: [private]] export bar: 1
Importing this module doesn't affect lib. Instead, its exports are collected into a private runtime library that is local to the module or user context that is importing this module, along with those of any other private modules that the target is importing, then imported to the target from there. The private runtime library is used for the same conflict resolution that lib is used for. The main runtime library lib takes precedence over the private lib, so don't count on the private lib overriding global things.
This kind of thing is useful for making utility modules, advanced APIs, or other such tricks. It is also useful for making strong-modular code which requires explicit imports, if that is what you're into.
It's worth noting that if your module doesn't actually export anything, there is no difference between a named private module or a named public module, so it's basically treated as public. All that matters is that it has a name. Which brings us to...
Unnamed Modules
As explained above, if your module doesn't have a name then it pretty much has to be treated as private. More than private though, since you can't tell if it's loaded, you can't upgrade it or even keep from reloading it. But what if that's what you want?
In some cases, you really want your code run for effect. In these cases having your code rerun every time is what you want to do. Maybe it's a script that you're running with do but structuring as a module to avoid leaking words. Maybe you're making a mixin, some utility functions that have some local state that needs initializing. It could be just about anything.
I frequently make my %rebol.r file an unnamed module because I want to have more control over what it exports and how. Plus, since it's done for effect and doesn't need to be reloaded or upgraded there's no point in giving it a name.
No need for a code example, your earlier ones will act this way.
I hope this gives you enough of an overview of the design of R3's module system.
I have created a small parser in c using flex and bison. The parser writes the result to some global variables and the caller function reads it from there.
I am trying to package my parser as a php extension. From what i understand from the php documentation true global variables are not recommended because they are not thread-safe and i have to use module globals instead.
In order to use module globals you have to pass in the function TSRMLS_DC as its last argument.
To you know if i can modify the yyparse to accept TSRMLS_DC as an argument. Or if there is another way to access global variable?
I wouldn't use global variables, but use a more modern parser generator that is also reentrant. Look for instance how I've done it for the meta extension (I use a slightly changed lemon and re2c).