如何实现预编译器指令像功能 [英] How to achieve precompiler directive like functionality

问题描述

我正在开发一个有角度的应用程序，建议对生产中运行的很多事情使用生成的代码，即模板缓存，表达式缓存和静态DI注入器。目前没有良好的方式在不同的构建配置之间切换，所以我使用的模式推荐

在lib / main.dart中，您可以看到正在导入的initializer-prod.dart文件有initializer-dev.dart对应。在这两个文件之间切换将允许您在prod和dev模式之间切换。您需要在使用prod模式之前运行生成器脚本。

这将导致以下导入：

  // import'initializer_prod.dart'as init; //在prod / test中使用。 
 import'initializer_dev.dart'as init; // Use in dev。 
  

如您所见，切换导入是一个手动过程。是否有更好的，更自动的方式来实现这一点？

解决方案

我看到两种可能性）

• 一个是使用变压器（另请参阅使用pub服务运行时将自定义参数传递到dart应用）

或

• 使用dart2js删除编译时死代码
  
  最近应该添加一个功能，pub构建允许使用命令行选项（如dart2js的-d）添加环境变量，

  log（String msg）{
 if （const String.fromEnvironment（'DEBUG'）！= null）{
 print（'debug：$ msg'）; 
} 
} 
 
 main（）{
 log（'在生产中，我不存在'）; 
} 
  

有关变压器的一些链接：

• 我们可以建造它？是，我们可以！


• 资产和变压器


• Day 992：搜索并替换Dart Transformer从聚合物中隐藏


• Dart Transformers for Polymer Cleanup


• Pub变压器


• dart2js_dransformer.dart


• 文档用户定义的变压器

EDIT

我可以在pubspec.yaml中配置 dart2js 选项，例如

< pre class =lang-yaml prettyprint-override> transformers：
- $ dart2js：
commandLineOptions：[-DDEBUG = true]
环境：
DEBUG：true
suppressWarnings：true
terse：true


如果提供了未知选项，或者不是预期的格式（ yaml list for commandLineOptions），则验证和 pub build yaml map 表单环境）

BUT String.fromEnvironment（）没有获得值

根据这个问题，这是支持的：
在pub构建期间将参数传递给dart2js

a href =https://code.google.com/p/dart/issues/detail?id=16298 =nofollow>如何将选项从pubspec.yaml传递到dart2js

EDIT-2

我试过了， strong>

 变压器：＃或dev_transformers 
  -  $ dart2js： 
环境：{PROD：true} 
  

p>

  String.fromEnvironment（）
 
 main（）{
 print（'PROD：$ {const String.fromEnvironment（'PROD'）}'）; 
 //在浏览器中工作
 //在Dartium中打印'PROD：null'
 //在Chrome中打印'PROD：true'
} 
  

另请参阅配置内置dart2js Transformer

EDIT-3

另一种方法是使用 assert 设置变量。
assert 在生产中被忽略。

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?

解决方案

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.

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