Rollup merge of #24548 - graydon:reference-tidying, r=steveklabnik
This just deletes some egregious lies and obsolete terminology -- all of which I originally wrote -- from the reference. I expect the reference itself will be deleted soon enough, but I found myself gritting teeth over these bits too much to let them into a 1.0 release.
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695efb53d6
3 changed files with 53 additions and 96 deletions
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@ -124,7 +124,7 @@ Yes. Calling C code from Rust is simple and exactly as efficient as calling C co
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Yes. The Rust code has to be exposed via an `extern` declaration, which makes it C-ABI compatible. Such a function can be passed to C code as a function pointer or, if given the `#[no_mangle]` attribute to disable symbol mangling, can be called directly from C code.
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## Why aren't function signatures inferred? Why only local slots?
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## Why aren't function signatures inferred? Why only local variables?
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* Mechanically, it simplifies the inference algorithm; inference only requires looking at one function at a time.
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* The same simplification goes double for human readers. A reader does not need an IDE running an inference algorithm across an entire crate to be able to guess at a function's argument types; it's always explicit and nearby.
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@ -5,8 +5,7 @@
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This document is the primary reference for the Rust programming language grammar. It
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provides only one kind of material:
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- Chapters that formally define the language grammar and, for each
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construct.
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- Chapters that formally define the language grammar.
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This document does not serve as an introduction to the language. Background
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familiarity with the language is assumed. A separate [guide] is available to
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@ -427,7 +426,7 @@ meta_seq : meta_item [ ',' meta_seq ] ? ;
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**FIXME:** grammar?
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A _declaration statement_ is one that introduces one or more *names* into the
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enclosing statement block. The declared names may denote new slots or new
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enclosing statement block. The declared names may denote new variables or new
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items.
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#### Item declarations
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@ -441,7 +440,7 @@ function, enumeration, structure, type, static, trait, implementation or module
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scope to a narrow region containing all of its uses; it is otherwise identical
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in meaning to declaring the item outside the statement block.
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#### Slot declarations
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#### Variable declarations
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```antlr
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let_decl : "let" pat [':' type ] ? [ init ] ? ';' ;
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@ -763,7 +762,7 @@ bound := path | lifetime
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### Memory ownership
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### Memory slots
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### Variables
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### Boxes
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@ -564,7 +564,7 @@ type_path_tail : '<' type_expr [ ',' type_expr ] + '>'
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A _path_ is a sequence of one or more path components _logically_ separated by
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a namespace qualifier (`::`). If a path consists of only one component, it may
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refer to either an [item](#items) or a [slot](#memory-slots) in a local control
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refer to either an [item](#items) or a [variable](#variables) in a local control
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scope. If a path has multiple components, it refers to an item.
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Every item has a _canonical path_ within its crate, but the path naming an item
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@ -735,13 +735,11 @@ Rust syntax is restricted in two ways:
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# Crates and source files
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Rust is a *compiled* language. Its semantics obey a *phase distinction*
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between compile-time and run-time. Those semantic rules that have a *static
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interpretation* govern the success or failure of compilation. We refer to
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these rules as "static semantics". Semantic rules called "dynamic semantics"
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govern the behavior of programs at run-time. A program that fails to compile
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due to violation of a compile-time rule has no defined dynamic semantics; the
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compiler should halt with an error report, and produce no executable artifact.
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Rust is a *compiled* language. Its semantics obey a *phase distinction* between
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compile-time and run-time. Those semantic rules that have a *static
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interpretation* govern the success or failure of compilation. Those semantics
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that have a *dynamic interpretation* govern the behavior of the program at
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run-time.
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The compilation model centers on artifacts called _crates_. Each compilation
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processes a single crate in source form, and if successful, produces a single
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@ -1064,9 +1062,9 @@ fn main() {}
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A _function item_ defines a sequence of [statements](#statements) and an
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optional final [expression](#expressions), along with a name and a set of
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parameters. Functions are declared with the keyword `fn`. Functions declare a
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set of *input* [*slots*](#memory-slots) as parameters, through which the caller
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passes arguments into the function, and an *output* [*slot*](#memory-slots)
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through which the function passes results back to the caller.
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set of *input* [*variables*](#variables) as parameters, through which the caller
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passes arguments into the function, and the *output* [*type*](#types)
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of the value the function will return to its caller on completion.
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A function may also be copied into a first-class *value*, in which case the
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value has the corresponding [*function type*](#function-types), and can be used
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@ -1229,7 +1227,7 @@ be undesired.
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#### Diverging functions
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A special kind of function can be declared with a `!` character where the
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output slot type would normally be. For example:
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output type would normally be. For example:
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```
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fn my_err(s: &str) -> ! {
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@ -1302,18 +1300,11 @@ contiguous stack segments like C.
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A _type alias_ defines a new name for an existing [type](#types). Type
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aliases are declared with the keyword `type`. Every value has a single,
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specific type; the type-specified aspects of a value include:
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specific type, but may implement several different traits, or be compatible with
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several different type constraints.
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* Whether the value is composed of sub-values or is indivisible.
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* Whether the value represents textual or numerical information.
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* Whether the value represents integral or floating-point information.
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* The sequence of memory operations required to access the value.
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* The [kind](#type-kinds) of the type.
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For example, the type `(u8, u8)` defines the set of immutable values that are
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composite pairs, each containing two unsigned 8-bit integers accessed by
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pattern-matching and laid out in memory with the `x` component preceding the
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`y` component:
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For example, the following defines the type `Point` as a synonym for the type
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`(u8, u8)`, the type of pairs of unsigned 8 bit integers.:
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```
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type Point = (u8, u8);
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@ -2551,7 +2542,7 @@ statements](#expression-statements).
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### Declaration statements
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A _declaration statement_ is one that introduces one or more *names* into the
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enclosing statement block. The declared names may denote new slots or new
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enclosing statement block. The declared names may denote new variables or new
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items.
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#### Item declarations
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@ -2566,18 +2557,18 @@ in meaning to declaring the item outside the statement block.
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> **Note**: there is no implicit capture of the function's dynamic environment when
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> declaring a function-local item.
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#### Slot declarations
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#### Variable declarations
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```{.ebnf .gram}
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let_decl : "let" pat [':' type ] ? [ init ] ? ';' ;
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init : [ '=' ] expr ;
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```
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A _slot declaration_ introduces a new set of slots, given by a pattern. The
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A _variable declaration_ introduces a new set of variable, given by a pattern. The
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pattern may be followed by a type annotation, and/or an initializer expression.
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When no type annotation is given, the compiler will infer the type, or signal
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an error if insufficient type information is available for definite inference.
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Any slots introduced by a slot declaration are visible from the point of
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Any variables introduced by a variable declaration are visible from the point of
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declaration until the end of the enclosing block scope.
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### Expression statements
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@ -2632,7 +2623,7 @@ of any reference that points to it.
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#### Moved and copied types
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When a [local variable](#memory-slots) is used as an
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When a [local variable](#variables) is used as an
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[rvalue](#lvalues,-rvalues-and-temporaries) the variable will either be moved
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or copied, depending on its type. All values whose type implements `Copy` are
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copied, all others are moved.
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call_expr : expr paren_expr_list ;
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```
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A _call expression_ invokes a function, providing zero or more input slots and
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an optional reference slot to serve as the function's output, bound to the
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`lval` on the right hand side of the call. If the function eventually returns,
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then the expression completes.
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A _call expression_ invokes a function, providing zero or more input variables
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and an optional location to move the function's output into. If the function
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eventually returns, then the expression completes.
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Some examples of call expressions:
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```
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Return expressions are denoted with the keyword `return`. Evaluating a `return`
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expression moves its argument into the output slot of the current function,
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destroys the current function activation frame, and transfers control to the
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caller frame.
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expression moves its argument into the designated output location for the
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current function call, destroys the current function activation frame, and
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transfers control to the caller frame.
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An example of a `return` expression:
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## Types
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Every slot, item and value in a Rust program has a type. The _type_ of a
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Every variable, item and value in a Rust program has a type. The _type_ of a
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*value* defines the interpretation of the memory holding it.
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Built-in types and type-constructors are tightly integrated into the language,
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* The machine-dependent integer and floating-point types.
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[^unittype]: The "unit" value `()` is *not* a sentinel "null pointer" value for
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reference slots; the "unit" type is the implicit return type from functions
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reference variables; the "unit" type is the implicit return type from functions
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otherwise lacking a return type, and can be used in other contexts (such as
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message-sending or type-parametric code) as a zero-size type.]
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`self` refers to the value of type `String` that is the receiver for a call to
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the method `make_string`.
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# The `Copy` trait
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# Special traits
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Rust has a special trait, `Copy`, which when implemented changes the semantics
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of a value. Values whose type implements `Copy` are copied rather than moved
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upon assignment.
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Several traits define special evaluation behavior.
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# The `Sized` trait
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## The `Copy` trait
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`Sized` is a special trait which indicates that the size of this type is known
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at compile-time.
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The `Copy` trait changes the semantics of a type implementing it. Values whose
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type implements `Copy` are copied rather than moved upon assignment.
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# The `Drop` trait
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## The `Sized` trait
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The `Sized` trait indicates that the size of this type is known at compile-time.
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## The `Drop` trait
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The `Drop` trait provides a destructor, to be run whenever a value of this type
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is to be destroyed.
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# Memory model
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A Rust program's memory consists of a static set of *items* and a *heap*.
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Immutable portions of the heap may be shared between threads, mutable portions
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may not.
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Immutable portions of the heap may be safely shared between threads, mutable
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portions may not be safely shared, but several mechanisms for effectively-safe
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sharing of mutable values, built on unsafe code but enforcing a safe locking
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discipline, exist in the standard library.
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Allocations in the stack consist of *slots*, and allocations in the heap
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Allocations in the stack consist of *variables*, and allocations in the heap
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consist of *boxes*.
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### Memory allocation and lifetime
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When a stack frame is exited, its local allocations are all released, and its
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references to boxes are dropped.
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### Memory slots
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### Variables
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A _slot_ is a component of a stack frame, either a function parameter, a
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[temporary](#lvalues,-rvalues-and-temporaries), or a local variable.
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A _variable_ is a component of a stack frame, either a named function parameter,
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an anonymous [temporary](#lvalues,-rvalues-and-temporaries), or a named local
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variable.
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A _local variable_ (or *stack-local* allocation) holds a value directly,
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allocated within the stack's memory. The value is a part of the stack frame.
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variable `y`).
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Methods that take either `self` or `Box<Self>` can optionally place them in a
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mutable slot by prefixing them with `mut` (similar to regular arguments):
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mutable variable by prefixing them with `mut` (similar to regular arguments):
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```
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trait Changer {
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local variables. Local variables can be used only after they have been
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initialized; this is enforced by the compiler.
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# Runtime services, linkage and debugging
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The Rust _runtime_ is a relatively compact collection of Rust code that
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provides fundamental services and datatypes to all Rust threads at run-time. It
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is smaller and simpler than many modern language runtimes. It is tightly
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integrated into the language's execution model of memory, threads, communication
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and logging.
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### Memory allocation
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The runtime memory-management system is based on a _service-provider
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interface_, through which the runtime requests blocks of memory from its
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environment and releases them back to its environment when they are no longer
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needed. The default implementation of the service-provider interface consists
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of the C runtime functions `malloc` and `free`.
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The runtime memory-management system, in turn, supplies Rust threads with
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facilities for allocating releasing stacks, as well as allocating and freeing
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heap data.
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### Built in types
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The runtime provides C and Rust code to assist with various built-in types,
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such as arrays, strings, and the low level communication system (ports,
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channels, threads).
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Support for other built-in types such as simple types, tuples and enums is
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open-coded by the Rust compiler.
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### Thread scheduling and communication
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The runtime provides code to manage inter-thread communication. This includes
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the system of thread-lifecycle state transitions depending on the contents of
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queues, as well as code to copy values between queues and their recipients and
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to serialize values for transmission over operating-system inter-process
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communication facilities.
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### Linkage
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# Linkage
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The Rust compiler supports various methods to link crates together both
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statically and dynamically. This section will explore the various methods to
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