mirror of
https://github.com/chubin/cheat.sheets
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34 lines
1.6 KiB
Plaintext
34 lines
1.6 KiB
Plaintext
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// Owned pointer – only one thing can ‘own’ this pointer at a time
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// This means that when the `Box` leaves its scope, it can be automatically deallocated safely.
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let mut mine: Box<i32> = Box::new(3);
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*mine = 5; // dereference
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// Here, `now_its_mine` takes ownership of `mine`. In other words, `mine` is moved.
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let mut now_its_mine = mine;
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*now_its_mine += 2;
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println!("{}", now_its_mine); // 7
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// println!("{}", mine); // this would not compile because `now_its_mine` now owns the pointer
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// Reference – an immutable pointer that refers to other data
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// When a reference is taken to a value, we say that the value has been ‘borrowed’.
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// While a value is borrowed immutably, it cannot be mutated or moved.
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// A borrow lasts until the end of the scope it was created in.
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let mut var = 4;
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var = 3;
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let ref_var: &i32 = &var;
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println!("{}", var); // Unlike `mine`, `var` can still be used
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println!("{}", *ref_var);
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// var = 5; // this would not compile because `var` is borrowed
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// *ref_var = 6; // this would not either, because `ref_var` is an immutable reference
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// Mutable reference
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// While a value is mutably borrowed, it cannot be accessed at all.
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let mut var2 = 4;
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let ref_var2: &mut i32 = &mut var2;
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*ref_var2 += 2; // '*' is used to point to the mutably borrowed var2
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println!("{}", *ref_var2); // 6 , // var2 would not compile.
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// ref_var2 is of type &mut i32, so stores a reference to an i32, not the value.
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// var2 = 2; // this would not compile because `var2` is borrowed.
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