Macro maybe_macro::maybe

macro_rules! maybe {
    ($i:ident if $e:expr) => { ... };
    ($i:ident if let $p:pat = $e:expr) => { ... };
}

The maybe macro.

This macro takes a name and then an if or if let statement. If the conditional is true or the pattern matches, the macro evaluates to Some. Otherwise, it evaluates to None.

What the macro will evaluate - that comes before the if statement - must be an identifier, it can't be any expression.

Using with if

// This will filter out every value greater than 10.
slice.iter().filter_map(|&x| maybe!(x if < 10))

Using with if let

// This will filter out all error values.
slice.iter().filter_map(|x| maybe!(x if let Ok(_) = x));

Note that ident you return can also come from destructuring in the pattern:

slice.iter().filter_map(|x| maybe!(inner if let Ok(inner) = x));