Attribute Macro layout 

#[layout]

Provide a default implementation of the Layout trait for a widget

This attribute macro may be used with the widget macro to provide an implementation of Layout.

The #[layout] attribute must follow the widget attribute (it is not a stand-alone macro). It does not need to be imported (it is resolved by widget).

Overriding provided fns

This macro implements MacroDefinedLayout for the widget and adjusts the default implementations of each Layout method to call the corresponding MacroDefinedLayout method. The user may instead provide a direct implementation of any Layout method; this implementation may or may not call the corresponding MacroDefinedLayout method.

Layout syntax

Syntax is as follows:

Item: MemberItem Call* | LitItem Call* | MacroItem Call* | ExprItem
   A single item

MemberItem: self . Member
   A reference to a field (e.g. self.label or self.0); this field must be a #[widget].

LitItem: StrLit
   A string literal (e.g. "Hello world"). This implicitly constructs a widget roughly equivalent to Label<'static str> but without text wrapping.

MacroItem: (frame | column | row | list | float | grid) ! MacroArgs
   These layout macros are natively supported in layout syntax. They are equivalent to the like-named macros in kas::widgets aside from name resolution.

ExprItem: Expr
   An expression yielding a widget, e.g. Label::new("Hello world"). The result must be an object of some type W: Widget<Data = ()>. This widget will be stored in a hidden field and is accessible through Tile::get_child but does not receive input data.

Call : (. (align | pack | with_stretch | with_margin_style) MethodArgs)
   A method call modifying layout.