Ruby on Rails - Ruby Operator Precedence - Parentheses -

the following code results in error

example 1

if params[:id] == '2' || params.has_key? :id   abort('params id = 2 or nothing') end   syntax error, unexpected tsymbeg, expecting keyword_then or ';' or '\n' if params[:id] == '2' || params.has_key? :id 

however, switching conditional statements || adding parentheses works 100%.

example 2

if params.has_key? :id || params[:id] == '2'    abort('params id = 2 or nothing') end 

example 3

if (params[:id] == '2') || (params.has_key? :id)   abort('params id = 2 or nothing') end 

can explain me why example 1 result in error ?

thanks

your problem happening at:

params[:id] == '2' || params.has_key? :id 

which can simplified to:

:foo || some_method :bar 

which causes same error. expression in principle, ambiguous between

(:foo || some_method) :bar         (1) 

and

:foo || (some_method :bar)         (2) 

when expression ambiguous, resolved other factors. 1 factor, operator precedence tells nothing here disambiguating between (1) , (2). next factor linear order. since || appears before argument application () (omitted) in expression in question, former applies before latter. therefore, expression interpreted (1). since (:foo || some_method) parsed expression, there 2 expressions next each other. ungrammatical, as:

:baz :bar 

is ungrammatical.

in fact, if switch order as:

some_method :bar || :foo 

then, interpreted as

(some_method :bar) || :foo 

for same reason, , syntax error disappear.

also when resolve ambiguity explicitly using parentheses indicate argument application:

:foo || some_method(:bar) 

then there no ambiguity needed resolved, , syntax error disappears.