I am not able to understand the following line of code.

Its right there in Basic debugging checklist , B::Deparse

$ perl -MO=Deparse,-p -e " use constant X => 1/3; "
use constant ('X', 0.33333333333333331);
-e syntax OK
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When you're not sure about perl syntax, get App::PPI::Dumper

ppi_dumper / wxPPIxregexplain.pl

$ cat 2
use constant X => 1/3;


$ ppi_dumper 2
PPI::Document
  PPI::Statement::Include
    PPI::Token::Word    'use'
    PPI::Token::Whitespace      ' '
    PPI::Token::Word    'constant'
    PPI::Token::Whitespace      ' '
    PPI::Token::Word    'X'
    PPI::Token::Whitespace      ' '
    PPI::Token::Operator        '=>'
    PPI::Token::Whitespace      ' '
    PPI::Token::Number          '1'
    PPI::Token::Operator        '/'
    PPI::Token::Number          '3'
    PPI::Token::Structure       ';'
  PPI::Token::Whitespace        '\n'
  PPI::Token::Whitespace        '\n'
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So what is  =>? Its an PPI::Token::Operator ... see perlop