Folding expressions missing parenthesis

[nitnelave]

When expanding folding expressions, the generated code doesn't have parenthesis even though they are needed for some (most?) operators.

In the example, the expression is interpreted as (0 - (0 - 5)) which is 5, but written on the right as 0 - 0 - 5 which is -5.

See https://cppinsights.io/lnk?code=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&rev=1.0

[andreasfertig]

Hello nitnelave,

thanks for reporting this, quite interesting. I briefly looked into it and in the AST at this point there are no parentheses. I need to look deeper into it to figure out what I can do.

[andreasfertig]

Hello @nitnelave,

it looks like I finally understood it. I believe that this is a special case with fold expression. Their pattern is specified in the standard [temp.variadic] p10.1 - p10.2. Hence it does not require parentheses. A patch is on its way to add them in case of + or -.