Enum Layout 

#[non_exhaustive]
pub enum Layout {
    Auto,
    Single,
    Direct,
}

How the generated trampoline holds the item (layout = .., advanced).

The default, Layout::Auto, is the right choice almost always.

Variants (Non-exhaustive)

Non-exhaustive enums could have additional variants added in future. Therefore, when matching against variants of non-exhaustive enums, an extra wildcard arm must be added to account for any future variants.

Auto

Layout::Direct for a small item, Layout::Single for a large one (more than SINGLE_COPY_THRESHOLD tokens with its META).

Single

The item is held once, so the macro’s metadata is about the size of one item, and one call takes three expansions (two through the derive route) instead of one.

Direct

One expansion per call; the item is copied into each of the macro’s three output arms.

Trait Implementations

impl Clone for Layout

fn clone(&self) -> Self

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Copy for Layout

impl Debug for Layout

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Eq for Layout

impl PartialEq for Layout

fn eq(&self, other: &Self) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl StructuralPartialEq for Layout