Andrey Breslav
74 lines
2.3 KiB
Plaintext
74 lines
2.3 KiB
Plaintext
_Packages_ are containers for [classes|Classes and Inheritance], [objects|Object expressions and Declarations], [functions|Functions] and [properties|Properties And Fields]. A Kotlin package is _something like_ a package in *Java*, but it is not tied up to any physical file-system entity.
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h3. Root package
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Every [module|Modules and Compilation] declares a unique _root package_, that contains all the packages declared in this module.
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h3. Header package declaration
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A source file may start with a _header package declaration_ (see [the grammar|Grammar#packageHeader]):
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{jet}
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package foo.bar
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// ...
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{jet}
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All the contents of the source file are (directly or indirectly) contained by its header package. If the header is not specified, the module's root package is used.
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h3. Imports
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Besides the [default imports|Modules and Compilation#Default imports] declared by the module, each file may contain its own import directives.
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Syntax for imports is described [here|Grammar#import].
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One can import either a single name, e.g.
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{jet}
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import foo.Bar // Bar is now accessible withou qualification
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{jet}
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or all the accessible contents of a scope (package, class, object etc):
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{jet}
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import foo.* // everything in 'foo' becomes accessible
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{jet}
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If there is a name clash, one can disambiguate by using {{as}} keyword to locally rename the clashing entity:
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{jet}
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import foo.Bar // Bar is accessible
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import bar.Bar as bBar // bBar stands for 'bar.Bar'
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{jet}
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h3. Absolute and relative names
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Consider the following example (syntax is fictional):
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{jet}
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package a {
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package b {
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val x = 1
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package a {
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val y = a.b.x // Problem
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}
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}
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}
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{jet}
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At the line marked "Problem" we have the following potential ambiguity: what does {{a}} stand for: the outer *package* {{a}} or the inner one? The rule here is that names are always _relative_: {{a}} is resolved in its scope of occurrence that makes it mean the inner *package* {{a}}, so this code does not compile.
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To fix it, we need an _absolute_ name. These start with the *package* keyword:
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{jet}
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package a {
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package b {
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val x = 1
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package a {
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val y = package.root.a.b.x // Fixed
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}
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}
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}
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{jet}
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In this example, we assumed that the root package of our module is named {{root}}.
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Absolute names may be used in imports as well:
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{jet}
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import package.root.a.b.a.*
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{jet}
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h3. What's next
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* [Functions] |