redundant_closure_call false positive in macros

[tormol]

Is there a better way to delegate the body of a method to a parameter?

[kornelski]

I've ran into the same problem. I use a closure in a macro to work around macro hygiene and pass variables to an expression provided by the macro caller.

macro_rules! … {
…
    for (s,d) in src.iter().zip(dst.iter_mut()) {
        ($fix)(s,d);
    }
…
}

[oli-obk]

I think it would be fine to simply not trigger the lint inside macros.

Note that you can write this without closures, by passing in the names of s and d as $s:ident and $d:ident to the macro. This should result it the same amount of code written at the macro invocation.

[Kixunil]

Hit this right now. Yes the macro could be rewritten to do it differently but I believe that passing a closure to macro is the most readable way to write it.

This problem can be bypassed by writing (($closure))(args) (use double parentheses) but making the lint saner should still be considered.

[jpmckinney]

Note that you can write this without closures, by passing in the names of s and d as $s:ident and $d:ident to the macro. This should result it the same amount of code written at the macro invocation.

So would this be something like:

macro_rules! mymacro {
    ( $s:ident, $d:ident, $fix:expr ) => {
…
        for ($s, $d) in src.iter().zip(dst.iter_mut()) {
            $fix;
        }
…
    };
}

where $fix (which as a closure might have been |s, d| ...) just becomes the ... part?

I believe that passing a closure to macro is the most readable way to write it.

I agree, this:

mymacro!(..., (|s, d| s + d))

is easier to read than:

mymacro!(..., s, d, s + d)

(especially as the s + d expression becomes longer, and as the number of arguments increases).

This problem can be bypassed by writing (($closure))(args) (use double parentheses) but making the lint saner should still be considered.

This worked for me, except because cargo fmt removes the doubling, I add one set of parens in the macro definition and another set of parens in the macro call.