=> is usually used to separate a hash key from a hash value. But it can be used istead of comma in other cases also.

It is often more readable to use the => operator between key/value pairs. The => operator is mostly just a more visually distinctive synonym for a comma, but it also arranges for its left-hand operand to be interpreted as a string -- if it's a bareword that would be a legal simple identifier (=> doesn't quote compound identifiers, that contain double colons). This makes it nice for initializing hashes.

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