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//! Declaration for the Keyword trait.
use crate::parse::rules;
use std::hash::Hash;
/// A Keyword identifies the possible types of a keyword for an Item.
///
/// These do not map one-to-one to Item strings: several Item strings
/// may be placed in a single Keyword -- for example, when their order
/// is significant with respect to one another, like "accept" and
/// "reject" in router descriptors.
///
/// Every keyword has an "index", which is a small number suitable for
/// indexing an array. These are used in Section and SectionRules.
///
/// Turning a string into a keyword cannot fail: there is always an
/// "UNRECOGNIZED" keyword.
///
/// See macro::decl_keyword! for help defining a Keyword type for a
/// network document.
pub(crate) trait Keyword:
crate::KeywordEncodable + Hash + Eq + PartialEq + Copy + Clone
{
/// Find a Keyword corresponding to a string that appears in a
/// network document.
fn from_str(s: &str) -> Self;
/// Try to find the keyword corresponding to a given index value,
/// as used in Section and SectionRules.
#[allow(unused)] // TODO keep Keyword::from_idx ?
fn from_idx(i: usize) -> Option<Self>;
/// Return the index for this keyword.
fn idx(self) -> usize;
/// Return the number of indices for this keyword.
fn n_vals() -> usize;
/// Return the "UNRECOGNIZED" keyword.
fn unrecognized() -> Self;
/// Return the "ANN_UNRECOGNIZED" keyword.
fn ann_unrecognized() -> Self;
/// Return true iff this keyword denotes an annotation.
fn is_annotation(self) -> bool;
/// Convert from an index to a human-readable string.
#[allow(unused)] // TODO keep Keyword::idx_to_str ?
fn idx_to_str(i: usize) -> &'static str {
Self::from_idx(i)
.map(|x| x.to_str())
.unwrap_or("<out of range>")
}
/// Return a new TokenFmtBuilder for creating rules about this keyword.
fn rule(self) -> rules::TokenFmtBuilder<Self> {
rules::TokenFmtBuilder::new(self)
}
}
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