Struct FieldFallback 

pub struct FieldFallback {
    pub get: LitStr,
    pub names: Option<LitStr>,
}

The fallback of the field readers of s3(r_data_accessors), s4(r_data_accessors) and env(r_data_accessors) (#2150): fallback = "Self::column", and optionally fallback_names = "Self::column_names", in the path style of #[r_data(get = "Self::f")].

fallback names a fn(&Self, name: &str) -> Option<T>, T: IntoR, which the readers call on the live Rust value for a name no field has, on the bare pointer (an S3 or env object’s classed pointer, an S4 object’s ptr); a list or environment carrying the pointer in .ptr keeps its own elements for those names. Fields win, a [[ position counts the fields only, names() / as.list() stay the fields, and an assignment to a name no field has is refused as before. None reads what an unknown name reads without the fallback: miniextendr_no_field on S3 (default lookup) and S4, NULL under lookup = "list" and on an env class (whose $ tries the methods before the fallback). The macro handles the Option itself, so Some(x) reads x and a scalar T is never NA for None.

fallback_names names a fn(&Self) -> Vec<String>: .DollarNames() offers its names after the fields (after the methods on an env class). Without it, completion offers the fields only.

The impl expansion emits one .Call entry for each (field_syntax::fallback_c_entries), so only one impl block of a type carries the option: it is not a class setting the blocks repeat (ParsedImpl::class_settings) but part of the class that block defines (ParsedImpl::class_definitions), next to the constructor.

Fields

get: LitStr

fallback = "Self::column": the path, as written.

names: Option<LitStr>

fallback_names = "Self::column_names", as written.

Trait Implementations

impl Clone for FieldFallback

fn clone(&self) -> Self

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for FieldFallback

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

Formats the value using the given formatter.

Layout

Note: Most layout information is completely unstable and may even differ between compilations. The only exception is types with certain repr(...) attributes. Please see the Rust Reference's “Type Layout” chapter for details on type layout guarantees.

Size: 16 bytes