Rust 如何使用&;调用方法;从同一类型的另一个方法内部执行mut self?
我有一个Rust 如何使用&;调用方法;从同一类型的另一个方法内部执行mut self?,rust,Rust,我有一个Scannerstruct,它实现了scan(&mut self)方法。看起来像这样 pub struct Scanner { input: String, output: Vec<String>, state: ScannerState, } impl Scanner { pub fn scan(&mut self) { self.state = ScannerState::CharMode; for
Scanner
struct,它实现了scan(&mut self)
方法。看起来像这样
pub struct Scanner {
input: String,
output: Vec<String>,
state: ScannerState,
}
impl Scanner {
pub fn scan(&mut self) {
self.state = ScannerState::CharMode;
for character in self.input.chars() {
match character {
i @ '0'...'9' => self.output.push(format!("Integer digit: {}", i)),
'+' => self.output.push("Addition operator: +".to_string()),
'-' => self.output.push("Subtraction operator: -".to_string()),
'*' => self.output.push("Multiplication operator: *".to_string()),
'/' => self.output.push("Division operator: /".to_string()),
'%' => self.output.push("Modulus operator: %".to_string()),
'^' => self.output.push("Exponent operator: ^".to_string()),
'=' => self.output.push("Assignment operator: =".to_string()),
';' => self.output.push("Statement terminator: ;".to_string()),
c @ 'a'...'z'| c @ 'A'...'Z'
=> self.output.push(format!("Variable name: {}", c)),
' ' => self.output.push("Space, ignoring.".to_string()),
z @ _ => self.output.push(format!("Unrecognized token: {}", z))
}
}
}
}
但是等等!我们不能那样做,Rust告诉我们:
src/scanner.rs:34:17: 34:21 error: cannot borrow `*self` as mutable because `self.input` is also borrowed as immutable
src/scanner.rs:34 self.char_match(character);
^~~~
然而,我们的char\u match()
方法需要有一个对self
的可变引用,因为它推送,并且push()
在Vec
上执行需要可变性。那么,我的问题是,根据前面的知识,补救这种情况的理想方法是什么?
我是否只需要编写
scan()
作为一个长方法?char\u match
不需要对self
进行可变访问。对self.output
和self.state
的可变访问就足够了。如果您不授予它访问self.input
的权限,编译器将不再抱怨。我的建议是将char\u match
设置为无状态:
pub fn scan(&mut self) {
self.state = ScannerState::CharMode;
while self.state == ScannerState::CharMode {
for character in self.input.chars() {
match char_match(character) {
Some(string) => self.output.push(string),
None => self.state = ScannerState::QuitMode
}
}
self.state = ScannerState::Done;
}
}
fn char_match(c: char) -> Option<String> {
Some(match c {
'+' => "Addition operator: +".into(),
'-' => "Subtraction operator: -".into(),
'*' => "Multiplication operator: *".into(),
'/' => "Division operator: /".into(),
'%' => "Modulus operator: %".into(),
'^' => "Exponent operator: ^".into(),
'=' => "Assignment operator: =".into(),
';' => "Statement terminator: ;".into(),
' ' => "Space, ignoring.".into(),
'q' => return None,
i @ '0'...'9' => format!("Integer digit: {}", i),
c @ 'a'...'z' => format!("Variable name: {}", c),
z @ _ => format!("Unrecognized token: {}", z)
})
}
pub-fn扫描(&mut-self){
self.state=ScannerState::CharMode;
而self.state==ScannerState::CharMode{
对于self.input.chars()中的字符{
匹配字符\u匹配(字符){
Some(string)=>self.output.push(string),
无=>self.state=ScannerState::QuitMode
}
}
self.state=扫描状态::完成;
}
}
fn字符匹配(c:char)->选项{
一些(比赛c){
“+”=>“加法运算符:+”.into(),
“-”=>“减法运算符:-”.into(),
“*”=>“乘法运算符:*”.into(),
“/”=>“除法运算符:/”.into(),
“%”=>“模运算符:%”。into(),
“^'=>”指数运算符:^“,
“=”=>“赋值运算符:=”.into(),
“;”=>“语句终止符:;”.into(),
''=>“空格,忽略。“.into(),
'q'=>返回无,
i@'0'…'9'=>格式!(“整数位数:{},i),
c@'a'…'z'=>格式!(“变量名:{},c),
z@=>format!(“无法识别的标记:{}”,z)
})
}
这避免了完全借用,也更容易组合。
(对未来读者)避免在pub fn scan(&mut self) {
self.state = ScannerState::CharMode;
while self.state == ScannerState::CharMode {
for character in self.input.chars() {
match char_match(character) {
Some(string) => self.output.push(string),
None => self.state = ScannerState::QuitMode
}
}
self.state = ScannerState::Done;
}
}
fn char_match(c: char) -> Option<String> {
Some(match c {
'+' => "Addition operator: +".into(),
'-' => "Subtraction operator: -".into(),
'*' => "Multiplication operator: *".into(),
'/' => "Division operator: /".into(),
'%' => "Modulus operator: %".into(),
'^' => "Exponent operator: ^".into(),
'=' => "Assignment operator: =".into(),
';' => "Statement terminator: ;".into(),
' ' => "Space, ignoring.".into(),
'q' => return None,
i @ '0'...'9' => format!("Integer digit: {}", i),
c @ 'a'...'z' => format!("Variable name: {}", c),
z @ _ => format!("Unrecognized token: {}", z)
})
}