Macro dominator::box_fragment

macro_rules! box_fragment {
    () => { ... };
    (move { $($input:tt)* }) => { ... };
    ({ $($input:tt)* }) => { ... };
}

The same as fragment! except it returns a BoxFragment.

A BoxFragment can be stored in a struct or static:

static FOO: Lazy<BoxFragment> = Lazy::new(|| box_fragment!({ ... }));

fragment! is zero-cost, but box_fragment! is different: it has a performance cost, because it must heap-allocate the fragment and do dynamic dispatch.