Issue #11372 has been reported by Dug Dough.

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Misc #11372: Confusing a+b=9  ... unintented behavior, valid statement
https://bugs.ruby-lang.org/issues/11372

* Author: Dug Dough
* Status: Open
* Priority: Normal
* Assignee: 
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Hello, I found that when = is written instead of ==, it can cause unintended effects and it is hard to notice this typo, because it is valid statement.  For example valid statement a+b=7 ,due to the everything is a expression,  is treated  as a+(b=11) and not interpreted as syntax error, like in other languages.

Should't be this behavior changed?
My  suggestion is to make the assignment operator unable to be used as expresion (syntactically). It would prevent  that mistakes.
Optionally (for 'backward compatibility', or 'override'), assignment enclosed in parentheses would still be treated as expression , that would make a+(b=9) valid. The meaning of extra parentheses would mean "This is not mistake, i want to use the value of variable b as expression".



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