Complex classes like Lexer often do a lot of different things. To break such a class down, we need to identify a cohesive component within that class. A common approach to find such a component is to look for fields/methods that share the same prefixes, or suffixes. You can also have a look at the cohesion graph to spot any un-connected, or weakly-connected components.
Once you have determined the fields that belong together, you can apply the Extract Class refactoring. If the component makes sense as a sub-class, Extract Subclass is also a candidate, and is often faster.
While breaking up the class, it is a good idea to analyze how other classes use Lexer, and based on these observations, apply Extract Interface, too.
| 1 | <?php  | 
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| 19 | class Lexer  | 
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| 20 | { | 
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| 21 | /**  | 
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| 22 | * Whitespace tokens.  | 
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| 23 | */  | 
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| 24 | private const SPACE_TOKENS = [  | 
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| 25 | Token::T_SPACE,  | 
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| 26 | Token::T_COMMENT,  | 
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| 27 | Token::T_NEWLINE,  | 
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| 28 | ];  | 
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| 29 | |||
| 30 | /**  | 
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| 31 | * Tag map.  | 
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| 32 | */  | 
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| 33 | private const TAG_MAP = [  | 
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| 34 | ':' => Token::T_COLON,  | 
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| 35 | ';' => Token::T_SEMICOLON,  | 
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| 36 | '$' => Token::T_DOLLAR,  | 
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| 37 | '%%' => Token::T_MARK,  | 
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| 38 |         '%{'            => Token::T_BEGIN_INC, | 
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| 39 | '%}' => Token::T_END_INC,  | 
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| 40 | '%token' => Token::T_TOKEN,  | 
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| 41 | '%term' => Token::T_TOKEN,  | 
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| 42 | '%left' => Token::T_LEFT,  | 
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| 43 | '%right' => Token::T_RIGHT,  | 
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| 44 | '%nonassoc' => Token::T_NON_ASSOC,  | 
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| 45 | '%prec' => Token::T_PRECTOK,  | 
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| 46 | '%type' => Token::T_TYPE,  | 
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| 47 | '%union' => Token::T_UNION,  | 
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| 48 | '%start' => Token::T_START,  | 
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| 49 | '%expect' => Token::T_EXPECT,  | 
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| 50 | '%pure_parser' => Token::T_PURE_PARSER,  | 
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| 51 | ];  | 
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| 52 | |||
| 53 | /**  | 
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| 54 | * @var string  | 
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| 55 | */  | 
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| 56 | protected $buffer;  | 
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| 57 | |||
| 58 | /**  | 
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| 59 | * @var string  | 
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| 60 | */  | 
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| 61 | protected $fileName;  | 
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| 62 | |||
| 63 | /**  | 
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| 64 | * @var int  | 
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| 65 | */  | 
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| 66 | protected $line;  | 
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| 67 | |||
| 68 | /**  | 
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| 69 | * @var int  | 
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| 70 | */  | 
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| 71 | protected $offset;  | 
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| 72 | |||
| 73 | /**  | 
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| 74 | * @var Token  | 
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| 75 | */  | 
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| 76 | protected $currentToken;  | 
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| 77 | |||
| 78 | /**  | 
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| 79 | * @var Token  | 
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| 80 | */  | 
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| 81 | protected $backToken;  | 
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| 82 | |||
| 83 | /**  | 
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| 84 | * @var string  | 
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| 85 | */  | 
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| 86 | protected $backChar;  | 
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| 87 | |||
| 88 | /**  | 
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| 89 | * @var bool  | 
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| 90 | */  | 
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| 91 | protected $prevIsDollar;  | 
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| 92 | |||
| 93 | /**  | 
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| 94 | * @var string  | 
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| 95 | */  | 
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| 96 | protected $char;  | 
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| 97 | |||
| 98 | /**  | 
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| 99 | * @var string  | 
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| 100 | */  | 
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| 101 | protected $value;  | 
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| 102 | |||
| 103 | /**  | 
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| 104 | * @param string $code  | 
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| 105 | * @param string $filename  | 
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| 106 | */  | 
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| 107 | public function startLexing(string $code, string $filename = '')  | 
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| 114 | |||
| 115 | /**  | 
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| 116 | * @return void  | 
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| 117 | */  | 
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| 118 | protected function reset()  | 
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| 126 | |||
| 127 | /**  | 
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| 128 | * @throws LexingException  | 
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| 129 | * @throws ParseException  | 
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| 130 | *  | 
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| 131 | * @return Token  | 
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| 132 | */  | 
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| 133 | public function getToken(): Token  | 
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| 143 | |||
| 144 | /**  | 
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| 145 | * @throws LexingException  | 
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| 146 | */  | 
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| 147 | public function ungetToken()  | 
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| 155 | |||
| 156 | /**  | 
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| 157 | * @throws LexingException  | 
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| 158 | * @throws ParseException  | 
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| 159 | *  | 
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| 160 | * @return Token  | 
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| 161 | */  | 
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| 162 | public function peek(): Token  | 
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| 169 | |||
| 170 | /**  | 
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| 171 | * @throws LexingException  | 
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| 172 | * @throws ParseException  | 
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| 173 | *  | 
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| 174 | * @return Token  | 
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| 175 | */  | 
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| 176 | public function getRawToken()  | 
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| 208 | |||
| 209 | /**  | 
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| 210 | * @throws LexingException  | 
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| 211 | *  | 
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| 212 | * @return bool  | 
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| 213 | */  | 
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| 214 | protected function isWhitespace(): bool  | 
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| 228 | |||
| 229 | /**  | 
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| 230 | * @return bool  | 
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| 231 | */  | 
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| 232 | protected function isNewline(): bool  | 
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| 242 | |||
| 243 | /**  | 
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| 244 | * @throws LexingException  | 
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| 245 | * @throws ParseException  | 
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| 246 | *  | 
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| 247 | * @return bool  | 
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| 248 | */  | 
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| 249 | protected function isComment(): bool  | 
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| 292 | |||
| 293 | /**  | 
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| 294 | * @return bool  | 
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| 295 | */  | 
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| 296 | protected function isEof(): bool  | 
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| 306 | |||
| 307 | /**  | 
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| 308 | * @throws LexingException  | 
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| 309 | * @throws ParseException  | 
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| 310 | *  | 
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| 311 | * @return int  | 
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| 312 | */  | 
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| 313 | protected function detectToken()  | 
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| 393 | |||
| 394 | /**  | 
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| 395 | * @return string  | 
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| 396 | */  | 
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| 397 | protected function getChar(): string  | 
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| 418 | |||
| 419 | /**  | 
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| 420 | * @param string $char  | 
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| 421 | *  | 
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| 422 | * @throws LexingException  | 
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| 423 | */  | 
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| 424 | protected function ungetChar(string $char)  | 
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| 436 | |||
| 437 | /**  | 
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| 438 | * @param int $type  | 
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| 439 | * @param string $value  | 
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| 440 | *  | 
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| 441 | * @return Token  | 
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| 442 | */  | 
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| 443 | protected function token(int $type, string $value): Token  | 
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| 447 | }  | 
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| 448 |