Yes, I read dart import and part of directives in same file
I have this structure:
I'm trying to achieve this behavior:
There is a problem. For some weird reason I can't use any directive with 'part of'. So I can't use this in the one.dart
:
part of mylib;
import 'SomeClass.dart';
//somecode
So I either need to move class definition from SomeClass.dart
to one.dart
(and that will make code less readable and mixed up) or I need to move 'import' in the mylib.dart
.
library mylib;
import 'SomeClass.dart';
part ..
I don't like either of the options. In the second case I will need to parse all modules then and move import/exports. Which will definitely break something.
It may sound weird but the project will build from various modules automatically. And one/
is one of them.
This app design is bad, I know. But either I need to find a better way or just make all variables public and don't bother.
Dart provides the part keyword to allow you to split code into separate files in a library. It's used in the same file as the library keyword and needs to provide a relative path to the other source files that make up the library: for example, part "functions. dart"; . You can create new, empty text files for classes.
When importing a library file from another package, use the the package: directive to specify the URI of that file. import 'package:utilities/utilities. dart'; When importing a library file from your own package, use a relative path when both files are inside of lib, or when both files are outside of lib.
What are the minimal requirements needed for a library in Dart? The minimal requirements for a library are: pubspec file. The pubspec. yaml file for a library is the same as for an application package—there is no special designation to indicate that the package is a library.
Default to defining one type per file, not using part
, and importing only the files you need. This covers the majority of use cases.
Now, let's say you have two types that are commonly used together - for example, a Thing
and a ThingException
that gets thrown when Thing
does bad things. Importing both of these files everywhere is tedious, so you have three options with their own tradeoffs:
thing.dart
exports thing_exception.dart
. Importing thing.dart
gives the importing file access to both. thing_exception.dart
declares that it is 'part of' thing.dart
. Importing thing.dart
gives the importing file access to both files. For this simple type and its exception, your best bet is to use option 1. When the amount of code grows or the two types diverge in visibility, this option becomes less attractive. This puts options 2 and 3 are on the table.
When you have separate files, option 2 is often a better approach than options 3 because you maintain some flexibility - you could only import thing_exception.dart
and not thing.dart
. If you use option 3, you can't do this - you either import all of the parts or none of them. This is the error you are seeing when trying to do a part and import in the same file.
Option 3 becomes valuable when you the code is in the two files is highly dependent on one another and they need the ability to access private members of each other. This is less common.
When you have a bunch of files like this together, it becomes a 'library' in the more traditional sense. You declare a main library file (your my lib.dart
file) that exports files:
export 'public.dart';
export 'other_public.dart';
The bin
script imports the library as a whole, but it can't see anything that isn't explicitly exported from my_lib.dart
.
import 'package:mylib/mylib.dart';
Here's an example of a smallish package that uses all three of these options together for a good reference.
I think you will have better luck using import
, and export
with show
. (Use of part of
is now discouraged.)
Answers to this question may help you: When to use part/part of versus import/export in Dart?
Also the Creating library packages documentation: https://www.dartlang.org/guides/libraries/create-library-packages
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