Rust pointers: Difference between revisions
From wikinotes
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</blockquote><!-- Traits --> | </blockquote><!-- Traits --> | ||
== Box == | == Box<T> == | ||
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Box types let you represent ''recursive types'', where the total size is unknown at compile time,<br> | Box types let you represent ''recursive types'', where the total size is unknown at compile time,<br> | ||
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</syntaxhighlight> | </syntaxhighlight> | ||
</blockquote><!-- Box --> | </blockquote><!-- Box --> | ||
== Rc<T> == | |||
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</blockquote><!-- Rc<T> --> | |||
</blockquote><!-- Smart Pointers --> | </blockquote><!-- Smart Pointers --> | ||
Revision as of 00:24, 10 February 2023
Pointers/References
let foo = String::new("hi"); &foo // `&` get reference to foo let ref = &foo; *ref // `*` de-reference to get foo instance
Smart Pointers
The standard library implements some reusable smart-pointers to handle edge-cases.
Libraries may implment their own smart-pointers (and so can you).Pointer Relevant Traits
Box<T>
Box types let you represent recursive types, where the total size is unknown at compile time,
by replacing your type with a pointer to it.The docs use the example of a recursive enum.
An Enum's size is determined by it's largest possible value.
If an enum refers to an instance of itself the compiler is unable to determine it's size.The box type allocates your object to the heap, and returns a pointer to it.
Pointers have a known size, so you can assign that instead.
Also, it implements the Deref trait, which allows you to use box as if it were a reference to the object you assigned to it.#[derive(Debug)] enum Path { Dir(String, Box<Path>), File(String), } impl Path { fn file(file: &str) -> Box<Path> { Box::new( Path::File(file.to_string()) ) } fn dir(dir: &str, path: Box<Path>) -> Box<Path> { Box::new( Path::Dir(dir.to_string(), path) ) } } fn main() { let mypath = Path::dir("/var", Path::dir("/tmp", Path::file("/foo.txt"))); dbg!(mypath); }Rc<T>