First of all: I am fully aware of this post: Cannot infer appropriate lifetime for autoref in Iterator impl and that the problem is probably similar to mine. However, I can't get it working with the knowledge of this thread.
The code:
use std::str::Chars;
use super::token::*;
use super::token_stream::TokenStream;
pub struct Lexer<'a> {
input: Chars<'a>,
buffer: String,
cur_char: char
}
impl<'a> Lexer<'a> {
pub fn new(iterator: Chars<'a>) -> Lexer {
let mut lexer = Lexer {
input: iterator,
buffer: String::new(),
cur_char: '\0' };
lexer.consume_next();
lexer
}
pub fn new_from_str(content : &str) -> Lexer {
Lexer::new(content.chars())
}
fn consume_next(&mut self) -> char {
let next = self.input.next();
if let Some(c) = next {
self.buffer.push(c);
self.cur_char = c;
}
else {
self.cur_char = '\0';
}
self.current_char()
}
fn clear_buffer(&mut self) {
self.buffer.clear();
}
fn current_char(&self) -> char {
self.cur_char
}
fn scan_line_comment(&self) -> Token { Token::EndOfFile }
fn scan_multi_line_comment(&self) -> Token { Token::EndOfFile }
fn scan_identifier(&self) -> Token { Token::EndOfFile }
fn scan_char_literal(&self) -> Token { Token::EndOfFile }
fn scan_string_literal(&self) -> Token { Token::EndOfFile }
fn scan_number_literal(&self) -> Token { Token::EndOfFile }
fn consume_and_return<'b>(&mut self, token: Token<'b>) -> Token<'b> {
self.consume_next();
token
}
}
impl<'a> TokenStream for Lexer<'a> {
fn next_token(&mut self) -> Token {
match self.current_char() {
/* Skip whitespace */
' ' |
'\r' |
'\n' |
'\t' => {
self.clear_buffer();
self.consume_and_return(Token::Whitespace)
}
/* Opening delimiters */
'(' => self.consume_and_return(Token::OpenDelim(DelimitToken::Paren)),
'[' => self.consume_and_return(Token::OpenDelim(DelimitToken::Bracket)),
'{' => self.consume_and_return(Token::OpenDelim(DelimitToken::Brace)),
/* Opening delimiters */
')' => self.consume_and_return(Token::CloseDelim(DelimitToken::Paren)),
']' => self.consume_and_return(Token::CloseDelim(DelimitToken::Bracket)),
'}' => self.consume_and_return(Token::CloseDelim(DelimitToken::Brace)),
/* Special tokens which aren't the beginning
of any other token */
'?' => self.consume_and_return(Token::Question),
';' => self.consume_and_return(Token::SemiColon),
',' => self.consume_and_return(Token::Comma),
/* Dot, DotDot and DotDotDot tokens */
'.' => match self.consume_next() {
'.' => match self.consume_next() {
'.' => self.consume_and_return(Token::DotDotDot),
_ => Token::DotDot
},
_ => Token::Dot
},
/* Tokens starting with '+' */
'+' => match self.consume_next() {
'=' => self.consume_and_return(Token::BinOpEq(BinOpToken::Plus)),
_ => Token::BinOp(BinOpToken::Plus)
},
/* Tokens starting with '-' */
'-' => match self.consume_next() {
'=' => self.consume_and_return(Token::BinOpEq(BinOpToken::Minus)),
'>' => self.consume_and_return(Token::Arrow),
_ => Token::BinOp(BinOpToken::Minus)
},
/* Tokens starting with '*' */
'*' => match self.consume_next() {
'=' => self.consume_and_return(Token::BinOpEq(BinOpToken::Star)),
_ => return Token::BinOp(BinOpToken::Star)
},
/* Tokens starting with '/' */
'/' => match self.consume_next() {
'=' => self.consume_and_return(Token::BinOpEq(BinOpToken::Slash)),
'/' => self.scan_line_comment(),
'*' => self.scan_multi_line_comment(),
_ => Token::BinOp(BinOpToken::Slash)
},
/* Tokens starting with '%' */
'%' => match self.consume_next() {
'=' => self.consume_and_return(Token::BinOpEq(BinOpToken::Percent)),
_ => Token::BinOp(BinOpToken::Percent)
},
/* Tokens starting with '^' */
'^' => match self.consume_next() {
'=' => self.consume_and_return(Token::BinOpEq(BinOpToken::Caret)),
_ => return Token::BinOp(BinOpToken::Caret)
},
/* Tokens starting with '!' */
'!' => match self.consume_next() {
'=' => self.consume_and_return(Token::RelOp(RelOpToken::NotEq)),
_ => Token::Exclamation
},
/* Tokens starting with '=' */
'=' => match self.consume_next() {
'=' => self.consume_and_return(Token::RelOp(RelOpToken::EqEq)),
_ => Token::Eq
},
/* Tokens starting with '&' */
'&' => match self.consume_next() {
'&' => self.consume_and_return(Token::LogicalOp(LogicalOpToken::AndAnd)),
'=' => self.consume_and_return(Token::BinOpEq(BinOpToken::And)),
_ => Token::BinOp(BinOpToken::And)
},
/* Tokens starting with '|' */
'|' => match self.consume_next() {
'|' => self.consume_and_return(Token::LogicalOp(LogicalOpToken::OrOr)),
'=' => self.consume_and_return(Token::BinOpEq(BinOpToken::Or)),
_ => Token::BinOp(BinOpToken::Or)
},
/* Tokens starting with '<' */
'<' => match self.consume_next() {
'<' => match self.consume_next() {
'=' => self.consume_and_return(Token::BinOpEq(BinOpToken::Shl)),
_ => Token::BinOp(BinOpToken::Shl)
},
'=' => self.consume_and_return(Token::RelOp(RelOpToken::LessEq)),
_ => Token::RelOp(RelOpToken::LessThan)
},
/* Tokens starting with '>' */
'>' => match self.consume_next() {
'>' => match self.consume_next() {
'=' => self.consume_and_return(Token::BinOpEq(BinOpToken::Shr)),
_ => Token::BinOp(BinOpToken::Shr)
},
'=' => self.consume_and_return(Token::RelOp(RelOpToken::GreaterEq)),
_ => Token::RelOp(RelOpToken::GreaterThan)
},
/* Char and string literals */
'\'' => self.scan_char_literal(),
'\"' => self.scan_string_literal(),
/* Integer- and float literals and identifiers */
'0' ... '9' => self.scan_number_literal(),
'a' ... 'z' |
'A' ... 'Z' => self.scan_identifier(),
/* When end of iterator has been reached */
_ => Token::EndOfFile
}
}
}
impl<'a> Iterator for Lexer<'a> {
type Item = Token<'a>;
fn next(&mut self) -> Option<Self::Item> {
let token = self.next_token();
match token {
Token::EndOfFile => None,
_ => Some(token)
}
}
}
#[cfg(test)]
mod tests {
use super::*;
use super::super::token::*;
use super::super::token_stream::TokenStream;
#[test]
fn simple_tokens() {
let solution = [
Token::OpenDelim(DelimitToken::Paren),
Token::CloseDelim(DelimitToken::Paren),
Token::OpenDelim(DelimitToken::Bracket),
Token::CloseDelim(DelimitToken::Bracket),
Token::OpenDelim(DelimitToken::Brace),
Token::CloseDelim(DelimitToken::Brace),
Token::Question,
Token::SemiColon,
Token::Comma,
Token::EndOfFile
];
let mut lexer = Lexer::new_from_str("()[]{}?;,");
for expected in &solution {
assert_eq!(lexer.next_token(), *expected);
}
}
}
And its dependent module 'Token':
#[derive(Clone, PartialEq, Eq, Hash, Debug, Copy)]
pub enum BinOpToken {
Plus, // +
Minus, // -
Star, // *
Slash, // /
Percent, // %
Caret, // ^
And, // &
Or, // |
Shl, // <<
Shr // >>
}
#[derive(Clone, PartialEq, Eq, Hash, Debug, Copy)]
pub enum RelOpToken {
EqEq, // ==
NotEq, // !=
LessThan, // <
LessEq, // <=
GreaterThan, // >
GreaterEq // >=
}
#[derive(Clone, PartialEq, Eq, Hash, Debug, Copy)]
pub enum LogicalOpToken {
AndAnd, // &&
OrOr // ||
}
#[derive(Clone, PartialEq, Eq, Hash, Debug, Copy)]
pub enum DelimitToken {
Paren, // ( or )
Bracket, // [ or ]
Brace, // { or }
}
#[derive(Clone, PartialEq, Eq, Hash, Debug, Copy)]
pub enum LiteralToken<'a> {
Char(&'a str), // e.g. 'a'
Integer(&'a str), // e.g. 5, 42, 1337, 0
Float(&'a str), // e.g. 0.1, 5.0, 13.37, 0.0
String(&'a str) // e.g. "Hello, World!"
}
#[derive(Clone, PartialEq, Eq, Hash, Debug, Copy)]
pub enum Token<'a> {
/* Logical operators, e.g. && or || */
LogicalOp(LogicalOpToken),
/* Binary operators compatible with assignment, e.g. +, - */
BinOp(BinOpToken),
/* Binary assignment operators, e.g. +=, -= */
BinOpEq(BinOpToken),
/* Relational operators, e.g. <, <=, >, >=, ==, != */
RelOp(RelOpToken),
/* An opening delimiter, e.g. { or ( or [ */
OpenDelim(DelimitToken),
/* A closing delimiter, e.g. } or ) or ] */
CloseDelim(DelimitToken),
/* Identifiers with their given name */
Identifier(&'a str),
/* Literal token, e.g. an integer, float or string literal */
Literal(LiteralToken<'a>),
/* Special tokens */
Eq, // =
Colon, // :
SemiColon, // ;
ColonColon, // ::
Dot, // .
DotDot, // ..
DotDotDot, // ...
Comma, // ,
Exclamation, // !
Question, // ?
Arrow, // ->
FatArrow, // =>
/* Junk tokens which the parser doesn't require in order to parse the program. */
Whitespace,
Comment,
/* End of file (EOF) token indicating the end of stream for parsing */
EndOfFile
}
As well as the trait 'TokenStream':
pub use super::token::Token;
pub trait TokenStream {
fn next_token(&mut self) -> Token;
}
I am getting the following error:
src/parser/lexer.rs:202:20: 202:32 error: cannot infer an appropriate lifetime for autoref due to conflicting requirements [E0495]
src/parser/lexer.rs:202 let token = self.next_token();
^~~~~~~~~~~~
I guess that it is a lifetime problem. My next_token() method returns a Token that has a lifetime independent of Self, however I am not sure if I did the annotation right.
I also tried to do some more annotation for the next() method in Iterator but it all failed ...
I get this error when I add a lifetime to the &mut self parameter of the next() method in the implementation of the Iterator trait:
src/parser/lexer.rs:201:2: 207:3 error: method `next` has an incompatible type for trait:
expected bound lifetime parameter ,
found concrete lifetime [E0053]
robbepop
I found a solution to my problems and now everything compiles fine.
The problem was in fact a lifetime problem but not only within the TokenStream trait. I had lifetime issues in several places across the entire code.
Some notable places from the long code in the initial post:
lexer.rs: line 46 - 58
fn scan_line_comment<'b>(&self) -> Token<'b> { Token::EndOfFile }
fn scan_multi_line_comment<'b>(&self) -> Token<'b> { Token::EndOfFile }
fn scan_identifier<'b>(&self) -> Token<'b> { Token::EndOfFile }
fn scan_char_literal<'b>(&self) -> Token<'b> { Token::EndOfFile }
fn scan_string_literal<'b>(&self) -> Token<'b> { Token::EndOfFile }
fn scan_number_literal<'b>(&self) -> Token<'b> { Token::EndOfFile }
fn consume_and_return<'b>(&mut self, token: Token<'b>) -> Token<'b> {
self.consume_next();
token
}
I had to insert the lifetime 'b to specify that the Token may outlive the Lexer instance.
The TokenStream required a new lifetime parameter so that it can specify that extended lifetime as well:
pub trait TokenStream<'a> {
fn next_token(&mut self) -> Token<'a>;
}
The TokenStream implementation for Lexer had to be adjusted for this change:
impl<'a, 'b> TokenStream<'b> for Lexer<'a> {
fn next_token(&mut self) -> Token<'b> {
...
}
...
}
As well as the Iterator implementation for Lexer
impl<'a> Iterator for Lexer<'a> {
type Item = Token<'a>;
fn next(&mut self) -> Option<Self::Item> {
let token = self.next_token();
match token {
Token::EndOfFile => None,
_ => Some(token)
}
}
}
That's it!
来源：https://stackoverflow.com/questions/35517514/error-cannot-infer-an-appropriate-lifetime-for-autoref-due-to-conflicting-requi