orlp
commented
4 years ago I'm sorry, I really, explicitly do not want to do this.
Closed ijackson closed 4 years ago
orlp
commented
4 years ago I'm sorry, I really, explicitly do not want to do this.
ijackson
commented
4 years ago That's a shame.
I found a way to do what I needed using only things which seem to me to be part of slotmap's stable API - specifically, the serde format. This saves me vendoring slotmap. I'm pasting the code here in case you would like to suggest a better way, and of course in case anyone else would like this. Astonishingly the magic of serde and rust means this monstrosity is only 10-15% slower than the method I provided in my MR.
//! Provides a [`get_idx_key`](trait.KeyDataExt.html#tymethod.get_idx_version) method on
//! `slotmap::KeyData`. See [KeyDataExt::get_idx_version].
/// Extension trait for `slotmap::KeyData`, providing `get_idx_version`.
///
/// No-one is expected to implement this trait for anything else.
pub trait KeyDataExt {
/// Returns the slot index and version. This is useful only in
/// unusual situations.
///
/// At any one time, a slotmap has at most one entry with each
/// index. The combination of index and version are unique across
/// time. Indices are generally not significantly bigger than thw
/// maximum ever occupancy. No other guarantees are made.
///
/// For serialisation, use `serde` or `as_ffi`.
///
/// ### panics: ###
///
/// This function panics if the `slotmap::KeyData` `serde::ser::Serialize`
/// representation has changed too much. This ought to be caught
/// by the tests, and would probably be a breaking change in the
/// underlying `slotmap` crate in any case.
///
/// If you prefer to receive an error rather than panicing,
/// see [keydata_extract].
fn get_idx_version(self) -> (u32, u32);
}
impl KeyDataExt for slotmap::KeyData {
fn get_idx_version(self) -> (u32, u32) {
keydata_extract(self).expect(
"slotmap KeyData Serialize representation changed!"
)
}
}
/// Underlying extraction function. Fails rather than panicing.
///
/// Fails if the `slotmap::KeyData` `serde::ser::Serialize`
/// representation has changed too much. Should not be able to fail
/// otherwise.
pub fn keydata_extract(key : slotmap::KeyData) -> Result<(u32, u32), Error> {
let mut m : MainExtractor = std::default::Default::default();
key.serialize(&mut m)?;
Ok(( m.idx .ok_or(error(line!()))?,
m.version.ok_or(error(line!()))? ))
}
#[derive(Debug)]
/// Problem with the `slotmap::KeyData` `Serialize` implementation.
///
/// Not really helpful. `Unexpected` gives the source line number
/// in `slotmap-slot-idx.rs`. `WasCustomSerialize` threw the
/// actual error away.
pub enum Error {
WasCustomSerialize,
Unexpected(std::num::NonZeroU32),
}
impl std::error::Error for Error { }
//---------- implementation. avert your eyes ----------
use serde::ser::{self,*};
use std::line;
use std::convert::TryFrom;
use std::fmt;
#[derive(Default)]
struct MainExtractor {
idx: Option<u32>,
version: Option<u32>,
}
struct ValueExtractor;
type R<Return> = Result<Return,Error>;
type ROk = R<()>;
use self::Error::*;
fn error(line: u32) -> Error { Unexpected(TryFrom::try_from(line).unwrap()) }
fn u<T>(line: u32) -> R<T> { Err(error(line)) }
type Imp = Impossible<(),Error>;
type RI = R<Imp>;
impl Serializer for &mut MainExtractor {
type Ok = ();
type Error = Error;
type SerializeStruct = Self;
type SerializeMap = Imp;
type SerializeSeq = Imp;
type SerializeTuple = Imp;
type SerializeTupleStruct = Imp;
type SerializeTupleVariant = Imp;
type SerializeStructVariant = Imp;
fn serialize_struct(self, _:&str, _: usize) -> R<Self> { Ok(self) }
fn serialize_bool (self, _: bool ) -> ROk { u(line!()) }
fn serialize_i8 (self, _: i8 ) -> ROk { u(line!()) }
fn serialize_i16 (self, _: i16 ) -> ROk { u(line!()) }
fn serialize_i32 (self, _: i32 ) -> ROk { u(line!()) }
fn serialize_i64 (self, _: i64 ) -> ROk { u(line!()) }
fn serialize_u8 (self, _: u8 ) -> ROk { u(line!()) }
fn serialize_u16 (self, _: u16 ) -> ROk { u(line!()) }
fn serialize_u32 (self, _: u32 ) -> ROk { u(line!()) }
fn serialize_u64 (self, _: u64 ) -> ROk { u(line!()) }
fn serialize_f32 (self, _: f32 ) -> ROk { u(line!()) }
fn serialize_f64 (self, _: f64 ) -> ROk { u(line!()) }
fn serialize_char (self, _: char ) -> ROk { u(line!()) }
fn serialize_str (self, _: &str ) -> ROk { u(line!()) }
fn serialize_bytes(self, _: &[u8 ]) -> ROk { u(line!()) }
fn serialize_none (self) -> ROk { u(line!()) }
fn serialize_unit (self) -> ROk { u(line!()) }
fn serialize_some<T>(self, _: &T) -> ROk
where T : Serialize + ?Sized { u(line!()) }
fn serialize_newtype_struct <T>(self, _:&str, _: &T) -> ROk
where T : Serialize + ?Sized { u(line!()) }
fn serialize_newtype_variant<T>(self, _:&str, _:u32, _:&str, _: &T) -> ROk
where T : Serialize + ?Sized { u(line!()) }
fn serialize_unit_struct (self,_:&str ) -> ROk { u(line!()) }
fn serialize_unit_variant(self,_:&str,_:u32,_:&str) -> ROk { u(line!()) }
fn serialize_seq (self,_:Option<usize> ) -> RI { u(line!()) }
fn serialize_tuple (self,_:usize ) -> RI { u(line!()) }
fn serialize_tuple_struct(self,_:&str, _:usize ) -> RI { u(line!()) }
fn serialize_map (self,_:Option<usize> ) -> RI { u(line!()) }
fn serialize_tuple_variant (self,_:&str,_:u32,_:&str,_:usize)->RI{u(line!())}
fn serialize_struct_variant(self,_:&str,_:u32,_:&str,_:usize)->RI{u(line!())}
}
impl SerializeStruct for &mut MainExtractor {
type Ok = ();
type Error = Error;
fn serialize_field<T: Serialize + ?Sized> (
&mut self, key: &str, value: &T
) -> R<()> {
if key == "idx" { self.idx = Some(value.serialize(ValueExtractor)?); }
if key == "version" { self.version = Some(value.serialize(ValueExtractor)?); }
Ok(())
}
fn end(self) -> ROk { Ok(()) }
}
type V = u32;
type ImpV = Impossible<V,Error>;
type RIV = R<ImpV>;
impl Serializer for ValueExtractor {
type Ok = V;
type Error = Error;
fn serialize_u32(self, value: u32) -> R<V> { Ok(value) }
type SerializeStruct = ImpV;
type SerializeMap = ImpV;
type SerializeSeq = ImpV;
type SerializeTuple = ImpV;
type SerializeTupleStruct = ImpV;
type SerializeTupleVariant = ImpV;
type SerializeStructVariant = ImpV;
fn serialize_bool (self, _: bool ) -> R<V> { u(line!()) }
fn serialize_i8 (self, _: i8 ) -> R<V> { u(line!()) }
fn serialize_i16 (self, _: i16 ) -> R<V> { u(line!()) }
fn serialize_i32 (self, _: i32 ) -> R<V> { u(line!()) }
fn serialize_i64 (self, _: i64 ) -> R<V> { u(line!()) }
fn serialize_u8 (self, _: u8 ) -> R<V> { u(line!()) }
fn serialize_u16 (self, _: u16 ) -> R<V> { u(line!()) }
fn serialize_u64 (self, _: u64 ) -> R<V> { u(line!()) }
fn serialize_f32 (self, _: f32 ) -> R<V> { u(line!()) }
fn serialize_f64 (self, _: f64 ) -> R<V> { u(line!()) }
fn serialize_char (self, _: char ) -> R<V> { u(line!()) }
fn serialize_str (self, _: &str ) -> R<V> { u(line!()) }
fn serialize_bytes(self, _: &[u8 ]) -> R<V> { u(line!()) }
fn serialize_none (self) -> R<V> { u(line!()) }
fn serialize_unit (self) -> R<V> { u(line!()) }
fn serialize_some <T>(self, _: &T) -> R<V>
where T : Serialize + ?Sized { u(line!()) }
fn serialize_newtype_struct <T>(self, _:&str, _: &T) -> R<V>
where T : Serialize + ?Sized { u(line!()) }
fn serialize_newtype_variant<T>(self, _:&str, _:u32, _:&str, _: &T) -> R<V>
where T : Serialize + ?Sized { u(line!()) }
fn serialize_unit_struct (self,_:&str ) -> R<V> { u(line!()) }
fn serialize_unit_variant (self,_:&str,_:u32,_:&str) -> R<V> { u(line!()) }
fn serialize_seq (self,_:Option<usize> ) -> RIV { u(line!()) }
fn serialize_tuple (self,_:usize ) -> RIV { u(line!()) }
fn serialize_tuple_struct (self,_:&str, _: usize ) -> RIV { u(line!()) }
fn serialize_struct (self,_:&str, _: usize ) -> RIV { u(line!()) }
fn serialize_map (self,_:Option<usize> ) -> RIV { u(line!()) }
fn serialize_tuple_variant (self,_:&str,_:u32,_:&str,_:usize)->RIV{u(line!())}
fn serialize_struct_variant(self,_:&str,_:u32,_:&str,_:usize)->RIV{u(line!())}
}
impl ser::Error for Error {
fn custom<T>(_msg: T) -> Self { return Error::WasCustomSerialize; }
}
impl fmt::Display for Error {
fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
fmt::Debug::fmt(self,f)
}
}
#[test]
fn check(){
fn t(v: u64) {
let kd = slotmap::KeyData::from_ffi(v);
let v = kd.as_ffi(); // KeyData is not transparent for all u64
let (idx,vsn) = self::KeyDataExt::get_idx_version(kd);
eprintln!("KeyData={:?} v=0x{:x?} idx={}=0x{:x} vsn={}=0x{:x}",
&kd, &v, idx,idx, vsn,vsn);
assert_eq!(v, ((vsn as u64) << 32) | (idx as u64));
}
t(0x0123456789abcdef);
t(0xfedcba9876543210);
t(0);
t(0xffffffff12345678);
t(0x12345678ffffffff);
t(0xffffffff00000000);
t(0x00000000ffffffff);
t(0x0000000012345678);
t(0x1234567800000000);
}
Hi. I really like this crate. Thanks.
I had one small issue that I think would be best addressed by adding a new getter on KeyData. My MR leaks the abstraction a bit more (about as much as the Debug impl does) but in my situation it would be quite useful. To motivate, I will explain:
I'm writing a game system. Players in a game may come and go but there will be few at any one time. I'm already using SlotMap for my record of the players.
I want to have something like a "player number" visible to the users: there's a player nickname but in one circumstance (a graphical representation) I really want something much terser. A small integer would be ideal. (Player 1 etc.)
Slotmap has that internally of course. But right now it's hidden. My options are 1. make a new data structure very similar to SlotMap 2. abuse KeyData.as_ffi 3. Add a method to get the slot index.
It seems to me that 3 is the right answer so here is my MR. I hope you like it. I wasn't quite sure what name and precise API you would like but this one seems OK to me. Returning the version as well is potentially a tiny bit wasteful and/or irrelevant, but it does make the doc exposition a lot easier.
I have noticed that DenseSlotMap doesn't seem to use index 0. I didn't add a guarantee that the index would be nonzero for a real entry. Should I add that to the doc?