I have a single file Dart program - let's say main.dart. I'm trying to provide some compile time environment values to it using --dart-define=env=env_value but in the Dart program, I'm always getting the default values.
This is what my Dart program looks like
void main() {
const myValue = const String.fromEnvironment("MY_VALUE", defaultValue: "DEFAULT");
print('My value: $myValue'); // Always prints "DEFAULT"
}
This is the command I'm using to run my program
dart main.dart --dart-define=MY_VALUE=SOME_VALUE
Now, when I include the exact same code from above in a Flutter app and run it with the below command, everything seems to work as expecetd but for some reason the above program always prints DEFAULT as the output on console.
flutter run --dart-define=MY_VALUE=SOME_VALUE
Is there something I'm missing when it comes to providing these values in a Dart program? I'm running macOS if that helps in any way.
If you type:
dart --help --verbose
It will give you the list of supported flags.
Usage: dart [<vm-flags>] <dart-script-file> [<script-arguments>]
Executes the Dart script <dart-script-file> with the given list of <script-arguments>.
Supported options:
...
--define=<key>=<value> or -D<key>=<value>
Define an environment declaration. To specify multiple declarations,
use multiple instances of this option.
...
So it appears that the flag you want is --define or -D, rather than --dart-define. Also note that this is considered a "vm-flag" and must come before the file name in order to work.
Therefore the following command should work:
dart --define=MY_VALUE=SOME_VALUE main.dart
Related
I am building a dart program to get the user input. when running the program using the run button I get the output in the output window but I cannot type in it. tried using the terminal to run the program and it worked well. so I want to know what is the right way to take the input from the user?
import 'dart:io';
void main() {
print("enter your name: ");
var name = stdin.readLineSync();
print("hello mrs ${name}");
}
From file -> Preferences -> Settings
search for "Dart: Cli Console"
Dart: Cli Console
Then change the drop-down menu into -terminal-
now you can run again your code and check
you can type in the terminal and your code will work.
In fact the right way using terminal as you did. It's not a fail. It's just how it works.
The answer regarding using the correct vs-code console is correct but you should also check out the dcli package and it's ask function.
Disclaimer: I'm the author of dcli.
I'm new to dart, and following the tutorial provided on the Dart for the web page.
It all makes sense - apart from one piece of sytax:
final InjectorFactory injector = self.injector$Injector;
Here's the full code from the tutorial:
import 'main.template.dart' as self;
const useHashLS = false;
#GenerateInjector([
routerProvidersHash,
ClassProvider(Client, useClass: InMemoryDataService),
// Using a real back end?
// Import 'package:http/browser_client.dart' and change the
above to:
// ClassProvider(Client, useClass: BrowserClient),
])
final InjectorFactory injector = self.injector$Injector;
void main() {
runApp(ng.AppComponentNgFactory, createInjector: injector);
}
I'm a confused by the apparent .method$Class syntax. Can anyone explain to me what this means/what it's doing?
It's also underlined in Webstorm with the message The getter 'injector$Injector' isn't defined for the class 'self'. Regardless, it runs fine and works as expected.
Thanks in advance!
$ in an identifier has no special meaning. It's by convention often used for names in generated code.
Angular also uses code generation and the code will only become available after code generation was executed for example by webdev serve or webdev build.
I don't know the current state but the code might still be generated in a directory that is not analyzed by the DartAnalyzler and you might always see the error even wen the app can be run without problems.
I'm trying to execute a simple erlang program of adding two numbers.
I'm trying to do this in Eclipse on Ubuntu 10.04 LTS.
When i execute this program, I'm getting the error as shown below:
** exception error: undefined function add:addfunc/0
How do i go about solving this error? Thanks in advance.
This program when executed in the erlang shell is working fine. But when it comes to eclipse it's giving me this error. Not this, any program for that matter is giving me the similar error. Guess I would be missing something about the eclipse configuration.
EDIT:
Anyways, This is the sample add program,
-module(add).
-export([addfunc/0]).
addfunc() ->
5 + 6.
This message tells you that module add doesn't have an exported function addfunc/0.
Ensure the function you want to be called has exactly that name, doesn't expect any
parameters, is
exported, the module is
compiled, the search path includes the compiled beam file and that there is no module clashes using code:clash()
Update
It's not clear how erlide (eclipse erlang plug-in you seem to use) compiles and runs a program. Try to compile source using erlc or inside erl shell. That way you'll have much easier controllable environment and you'll better understand what's going on.
I got exactly the same problem -for a tail recursive fibonacci function- below:
-module(math2).
-export([fibonacci/1]).
fibonacci(0) -> 0;
fibonacci(1) -> 1;
fibonacci(M) -> fibonacci(M-1) + fibonacci(M-2).
In the end, had realized that this is a compile-time exception. Then, have opened a new tab on my shell and tried with erlc, instead of erl.
$ erlc math2.erl
Now I am also able to see math2.beam file created.
Called fibonacci with 10:
4> math2:fibonacci(10).
55
and it worked!
I think you have not compiled the code and you are trying to run the program.
In eclipse, using the "Run" icon, trigger the run; which will get you to the erl shell in the console window.
There you do -
cd("C:\Learning_ERL\src").
And you should see output like-
(Learning-ERL#DALAKSHM-MNFSM)7> cd("C:\Learning_ERL\src").
c:/Learning_ERL/src
ok
Then compile the code -
c(add)
you should see something like this on the erl shell-
(Learning-ERL#DALAKSHM-MNFSM)10> c(add).
{ok,add}
Now you should be seeing a new file called - add.beam in the same directory as that of your erl source file - add.erl
add.beam is a bytecode file
Now you should be able to run the program without any error
How do you try to execute your code?
In your editor, right-click and choose "Run as"->"Erlang application". The VM that is launched will have your project loaded automatically and when editing/saving a file it will get reloaded. When launching, a console appears and you can call your code from there.
If it still doesn't work, what message do you get for m(add).?
This script (source code) can be perfectly executed in the production mode.
void main() {
int greeting = "Hello world!";
print(greeting);
}
This is a traditional hello world example that works fine in Dart.
The result is "Hello world!".
This script is self enough because not required other functionality and it works as expected.
Now I have small questions:
Can I consider that this script is valid and correct source code in Dart language becuase it works as expected?
If this script is valid source code in Dart language then why it cannot be executed in non-production mode?
If some code that can be perfectly executed in the production mode but cannot be executed in other mode then which mode in Dart more correct (production mode or other mode)?
P.S.
As a programmer, I am interesting not in theory and practice but I have interest only in answers in my small questions based on real example (even if it are very small).
If my questions are not so correct then I would like to know why?
Because they are directly related to programming in Dart language.
It is valid because types are ignored in production mode.
In checked mode (intended for development only) types are checked and you get an exception.
Types in Dart are not for runtime but for development time to make tools able to reason about the code and show possible bugs.
This means it doesn't matter if you type String or var. You cannot omit it completely because this violates the syntax.
It can be executed in production mode
# ~/dart/playground/bin/dart_valid
$ dart main.dart
Hello world!
It fails in checked mode (development mode)
# ~/dart/playground/bin/dart_valid
$ dart -c main.dart
Unhandled exception:
type 'String' is not a subtype of type 'int' of 'greeting'.
#0 main (file:///home/zoechi/source/my/dart/playground/bin/dart_valid/main.dart:2:18)
#1 _startIsolate.isolateStartHandler (dart:isolate-patch/isolate_patch.dart:216)
#2 _RawReceivePortImpl._handleMessage (dart:isolate-patch/isolate_patch.dart:115)
pub build fails because it uses the analyzer which utilizes type annotations like in checked mode and throws.
I'm developing an angular app, and it's recommended to use generated code for a lot of things running in production, namely template caches, expression caches, and a static DI injector. There's currently no nice way to switch between different build configurations, so I'm using the pattern recommended here:
In lib/main.dart you can see initializer-prod.dart file being imported, which has initializer-dev.dart counterpart. Switching between those two file will allow you to switch between prod and dev modes. You will need to run the generator script before using the prod mode.
This results in the following import:
//import 'initializer_prod.dart' as init; // Use in prod/test.
import 'initializer_dev.dart' as init; // Use in dev.
As you can see, switching the import is a manual process. Is there a better, more automatic way to achieve this?
I see two possibilities (haven't tried any of these myself yet)
one is to use a transformer (see also Pass custom parameters to a dart application when using pub serve to run it)
or
Compile-time dead code elimination with dart2js
Recently a feature should have been added that pub build allows adding an environment variables using a command line option (like dart2js's -d)
log(String msg) {
if (const String.fromEnvironment('DEBUG') != null) {
print('debug: $msg');
}
}
main() {
log('In production, I do not exist');
}
Some links about transformers:
Can We Build It? Yes, We Can!
Assets and Transformers
Day 992: Search and Replace Dart Transformer to Hide from Polymer
Dart Transformers for Polymer Cleanup
Pub transformers
dart2js_dransformer.dart
Document user-defined transformers
EDIT
I was able to configure dart2js options in pubspec.yaml like
transformers:
- $dart2js:
commandLineOptions: [-DDEBUG=true]
environment:
DEBUG: "true"
suppressWarnings: true
terse: true
They are validate and pub build fails if an unknown option is provided or if it's not the expected format (yaml list for commandLineOptions, yaml map form environment)
BUT String.fromEnvironment() didn't get a value
According to this issue, this is supported:
Passing in arguments to dart2js during pub build
I filed a bug How to pass options to dart2js from pubspec.yaml
EDIT-2
I tried it and it is working now:
transformers: # or dev_transformers
- $dart2js:
environment: { PROD: "true" }
access it from the code like
String.fromEnvironment()
main() {
print('PROD: ${const String.fromEnvironment('PROD')}');
// works in the browser
// prints 'PROD: null' in Dartium
// prints 'PROD: true' in Chrome
}
see also Configuring the Built-in dart2js Transformer
EDIT-3
Another way is to use assert to set variables.
assert is ignored in production.