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||=

The operator  || (OR) will return whatever value that is truthy first

Eg:
"abc" || "cde"
# return "abc" because it is truthy , and it return 'abc' without verifying 'cde'.

The operator && (AND) will return whatever value that is 'false' or 'nil' first

Eg:
nil && false
# return nil

false && nil
# return false

'abc' && 'cde'
# return 'cde' because 'abc' is truthy.


So the short-hand
name ||= 'default'

is equal to
name = name || 'default'

meaning that is name is not false or nil, then it is assigned back to name.
eg : if name is already 'John' then name = 'John'.

if name is false or nil, then || operator will evaluate the second part of OR operator, and return 'default' because it is truthy.



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