Trait Decoder

pub trait Decoder<'de>: Sized {
    type Cx: ?Sized + Context<Error = Self::Error, Mode = Self::Mode>;
    type Error;
    type Mode: 'static;
    type WithContext<'this, U>: Decoder<'de, Cx = U, Error = U::Error, Mode = U::Mode>
       where U: 'this + Context;
    type DecodeBuffer: AsDecoder<Cx = Self::Cx>;
    type DecodeSome: Decoder<'de, Cx = Self::Cx, Error = Self::Error, Mode = Self::Mode>;
    type DecodePack: SequenceDecoder<'de, Cx = Self::Cx>;
    type DecodeSequence: SequenceDecoder<'de, Cx = Self::Cx>;
    type DecodeMap: MapDecoder<'de, Cx = Self::Cx>;
    type DecodeMapEntries: EntriesDecoder<'de, Cx = Self::Cx>;
    type DecodeVariant: VariantDecoder<'de, Cx = Self::Cx>;

    // Required methods
    fn cx(&self) -> &Self::Cx;
    fn expecting(&self, f: &mut Formatter<'_>) -> Result;
    fn decode<T>(self) -> Result<T, Self::Error>
       where T: Decode<'de, Self::Mode>;
    fn decode_unsized<T, F, O>(self, f: F) -> Result<O, Self::Error>
       where T: ?Sized + DecodeUnsized<'de, Self::Mode>,
             F: FnOnce(&T) -> Result<O, <Self::Cx as Context>::Error>;
    fn decode_unsized_bytes<T, F, O>(self, f: F) -> Result<O, Self::Error>
       where T: ?Sized + DecodeUnsizedBytes<'de, Self::Mode>,
             F: FnOnce(&T) -> Result<O, <Self::Cx as Context>::Error>;

    // Provided methods
    fn with_context<U>(
        self,
        cx: &U,
    ) -> Result<Self::WithContext<'_, U>, <Self::Cx as Context>::Error>
       where U: Context { ... }
    fn skip(self) -> Result<(), <Self::Cx as Context>::Error> { ... }
    fn try_skip(self) -> Result<Skip, <Self::Cx as Context>::Error> { ... }
    fn decode_buffer(
        self,
    ) -> Result<Self::DecodeBuffer, <Self::Cx as Context>::Error> { ... }
    fn decode_empty(self) -> Result<(), <Self::Cx as Context>::Error> { ... }
    fn decode_bool(self) -> Result<bool, <Self::Cx as Context>::Error> { ... }
    fn decode_char(self) -> Result<char, <Self::Cx as Context>::Error> { ... }
    fn decode_u8(self) -> Result<u8, <Self::Cx as Context>::Error> { ... }
    fn decode_u16(self) -> Result<u16, <Self::Cx as Context>::Error> { ... }
    fn decode_u32(self) -> Result<u32, <Self::Cx as Context>::Error> { ... }
    fn decode_u64(self) -> Result<u64, <Self::Cx as Context>::Error> { ... }
    fn decode_u128(self) -> Result<u128, <Self::Cx as Context>::Error> { ... }
    fn decode_i8(self) -> Result<i8, <Self::Cx as Context>::Error> { ... }
    fn decode_i16(self) -> Result<i16, <Self::Cx as Context>::Error> { ... }
    fn decode_i32(self) -> Result<i32, <Self::Cx as Context>::Error> { ... }
    fn decode_i64(self) -> Result<i64, <Self::Cx as Context>::Error> { ... }
    fn decode_i128(self) -> Result<i128, <Self::Cx as Context>::Error> { ... }
    fn decode_usize(self) -> Result<usize, <Self::Cx as Context>::Error> { ... }
    fn decode_isize(self) -> Result<isize, <Self::Cx as Context>::Error> { ... }
    fn decode_f32(self) -> Result<f32, <Self::Cx as Context>::Error> { ... }
    fn decode_f64(self) -> Result<f64, <Self::Cx as Context>::Error> { ... }
    fn decode_array<const N: usize>(
        self,
    ) -> Result<[u8; N], <Self::Cx as Context>::Error> { ... }
    fn decode_bytes<V>(
        self,
        visitor: V,
    ) -> Result<V::Ok, <Self::Cx as Context>::Error>
       where V: UnsizedVisitor<'de, Self::Cx, [u8]> { ... }
    fn decode_string<V>(
        self,
        visitor: V,
    ) -> Result<V::Ok, <Self::Cx as Context>::Error>
       where V: UnsizedVisitor<'de, Self::Cx, str> { ... }
    fn decode_option(
        self,
    ) -> Result<Option<Self::DecodeSome>, <Self::Cx as Context>::Error> { ... }
    fn decode_pack<F, O>(self, f: F) -> Result<O, <Self::Cx as Context>::Error>
       where F: FnOnce(&mut Self::DecodePack) -> Result<O, <Self::Cx as Context>::Error> { ... }
    fn decode_sequence<F, O>(
        self,
        f: F,
    ) -> Result<O, <Self::Cx as Context>::Error>
       where F: FnOnce(&mut Self::DecodeSequence) -> Result<O, <Self::Cx as Context>::Error> { ... }
    fn decode_sequence_hint<F, O>(
        self,
        hint: &SequenceHint,
        f: F,
    ) -> Result<O, <Self::Cx as Context>::Error>
       where F: FnOnce(&mut Self::DecodeSequence) -> Result<O, <Self::Cx as Context>::Error> { ... }
    fn decode_map<F, O>(self, f: F) -> Result<O, <Self::Cx as Context>::Error>
       where F: FnOnce(&mut Self::DecodeMap) -> Result<O, <Self::Cx as Context>::Error> { ... }
    fn decode_map_hint<F, O>(
        self,
        _: &MapHint,
        f: F,
    ) -> Result<O, <Self::Cx as Context>::Error>
       where F: FnOnce(&mut Self::DecodeMap) -> Result<O, <Self::Cx as Context>::Error> { ... }
    fn decode_map_entries<F, O>(
        self,
        f: F,
    ) -> Result<O, <Self::Cx as Context>::Error>
       where F: FnOnce(&mut Self::DecodeMapEntries) -> Result<O, <Self::Cx as Context>::Error> { ... }
    fn decode_variant<F, O>(
        self,
        f: F,
    ) -> Result<O, <Self::Cx as Context>::Error>
       where F: FnOnce(&mut Self::DecodeVariant) -> Result<O, <Self::Cx as Context>::Error> { ... }
    fn decode_number<V>(
        self,
        visitor: V,
    ) -> Result<V::Ok, <Self::Cx as Context>::Error>
       where V: Visitor<'de, Self::Cx> { ... }
    fn decode_any<V>(
        self,
        visitor: V,
    ) -> Result<V::Ok, <Self::Cx as Context>::Error>
       where V: Visitor<'de, Self::Cx> { ... }
}

Trait governing the implementation of a decoder.

Required Associated Types

type Cx: ?Sized + Context<Error = Self::Error, Mode = Self::Mode>

Context associated with the decoder.

type Error

Error associated with decoding.

type Mode: 'static

Mode associated with decoding.

type WithContext<'this, U>: Decoder<'de, Cx = U, Error = U::Error, Mode = U::Mode> where U: 'this + Context

Decoder with a different context returned by Decoder::with_context

type DecodeBuffer: AsDecoder<Cx = Self::Cx>

Decoder returned by Decoder::decode_buffer.

type DecodeSome: Decoder<'de, Cx = Self::Cx, Error = Self::Error, Mode = Self::Mode>

Decoder returned by Decoder::decode_option.

type DecodePack: SequenceDecoder<'de, Cx = Self::Cx>

Decoder used by Decoder::decode_pack.

type DecodeSequence: SequenceDecoder<'de, Cx = Self::Cx>

Decoder returned by Decoder::decode_sequence.

type DecodeMap: MapDecoder<'de, Cx = Self::Cx>

Decoder returned by Decoder::decode_map.

type DecodeMapEntries: EntriesDecoder<'de, Cx = Self::Cx>

Decoder returned by Decoder::decode_map_entries.

type DecodeVariant: VariantDecoder<'de, Cx = Self::Cx>

Decoder used by Decoder::decode_variant.

Required Methods

fn cx(&self) -> &Self::Cx

Return the context associated with the decoder.

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

Format the human-readable message that should occur if the decoder was expecting to decode some specific kind of value.

Examples

use std::fmt;
use std::convert::Infallible;

use musli::Context;
use musli::de::{self, Decoder, Decode};

struct MyDecoder<'a, C: ?Sized> {
    cx: &'a C,
}

#[musli::decoder]
impl<'de, C: ?Sized + Context> Decoder<'de> for MyDecoder<'_, C> {
    type Cx = C;

    fn cx(&self) -> &C {
        self.cx
    }

    fn expecting(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "32-bit unsigned integers")
    }

    fn decode_u32(self) -> Result<u32, <Self::Cx as Context>::Error> {
        Ok(42)
    }
}

fn decode<T>(self) -> Result<T, Self::Error>

where T: Decode<'de, Self::Mode>,

Decode the current decoder into the value T.

This calls the appropriate Decode implementation for the given type.

fn decode_unsized<T, F, O>(self, f: F) -> Result<O, Self::Error>

where T: ?Sized + DecodeUnsized<'de, Self::Mode>, F: FnOnce(&T) -> Result<O, <Self::Cx as Context>::Error>,

Decode an unsized value by reference through the specified closure.

fn decode_unsized_bytes<T, F, O>(self, f: F) -> Result<O, Self::Error>

where T: ?Sized + DecodeUnsizedBytes<'de, Self::Mode>, F: FnOnce(&T) -> Result<O, <Self::Cx as Context>::Error>,

Decode an unsized value as bytes by reference through the specified closure.

Provided Methods

fn with_context<U>( self, cx: &U, ) -> Result<Self::WithContext<'_, U>, <Self::Cx as Context>::Error>

where U: Context,

Construct an decoder with a different context.

fn skip(self) -> Result<(), <Self::Cx as Context>::Error>

Skip over the current next value.

fn try_skip(self) -> Result<Skip, <Self::Cx as Context>::Error>

This is a variant of Decoder::skip, but instead of erroring in case skipping is not supported it must return Skip::Unsupported.

fn decode_buffer( self, ) -> Result<Self::DecodeBuffer, <Self::Cx as Context>::Error>

Buffer the current decoder into a buffer that can be used multiple times.

Buffering a decoder is necessary when additional introspection is needed to decode a type, but it also means that:

• The entire contents of the decoder needs to be dynamically buffered in memory.
• The in-memory representation might be lossy in some trivial ways. Such as arbitrary precision numbers being punted into a 64-bit float.

Examples

use musli::{Context, Decode, Decoder};
use musli::de::{AsDecoder, MapDecoder, EntryDecoder};
use musli::mode::Binary;

#[derive(Decode)]
struct Person {
    name: String,
    age: u32,
}

enum Enum {
    Empty,
    Person(Person),
}

impl<'de> Decode<'de, Binary> for Enum {
    fn decode<D>(cx: &D::Cx, decoder: D) -> Result<Self, D::Error>
    where
        D: Decoder<'de, Mode = Binary>,
    {
        let mut buffer = decoder.decode_buffer()?;

        let discriminant = buffer.as_decoder()?.decode_map(|st| {
            loop {
                let Some(mut e) = st.decode_entry()? else {
                    return Err(cx.missing_variant_tag("Enum"));
                };

                let found = e.decode_key()?.decode_unsized(|string: &str| {
                    Ok(string == "type")
                })?;

                if found {
                    break Ok(e.decode_value()?.decode()?);
                }
            }
        })?;

        match discriminant {
            0 => Ok(Enum::Empty),
            1 => Ok(Enum::Person(buffer.as_decoder()?.decode()?)),
            other => Err(cx.invalid_variant_tag("Enum", &other)),
        }
    }
}

fn decode_empty(self) -> Result<(), <Self::Cx as Context>::Error>

Decode a unit.

Examples

Deriving an implementation:

use musli::Decode;

#[derive(Decode)]
struct UnitStruct;

Implementing manually:

use musli::{Decode, Decoder};

impl<'de, M> Decode<'de, M> for UnitType {
    fn decode<D>(cx: &D::Cx, decoder: D) -> Result<Self, D::Error>
    where
        D: Decoder<'de>,
    {
        decoder.decode_empty()?;
        Ok(UnitType)
    }
}

fn decode_bool(self) -> Result<bool, <Self::Cx as Context>::Error>

Decode a boolean.

Examples

Deriving an implementation:

use musli::Decode;

#[derive(Decode)]
#[musli(packed)]
struct BooleanField {
    field: bool,
}

Implementing manually:

use musli::{Decode, Decoder};

impl<'de, M> Decode<'de, M> for BooleanField {
    fn decode<D>(cx: &D::Cx, decoder: D) -> Result<Self, D::Error>
    where
        D: Decoder<'de>,
    {
        Ok(Self {
            field: decoder.decode_bool()?,
        })
    }
}

fn decode_char(self) -> Result<char, <Self::Cx as Context>::Error>

Decode a character.

Examples

Deriving an implementation:

use musli::Decode;

#[derive(Decode)]
#[musli(packed)]
struct MyType {
    data: char,
}

Implementing manually:

use musli::{Decode, Decoder};

impl<'de, M> Decode<'de, M> for MyType {
    fn decode<D>(cx: &D::Cx, decoder: D) -> Result<Self, D::Error>
    where
        D: Decoder<'de>,
    {
        Ok(Self {
            data: decoder.decode_char()?,
        })
    }
}

fn decode_u8(self) -> Result<u8, <Self::Cx as Context>::Error>

Decode a 8-bit unsigned integer (a.k.a. a byte).

Examples

Deriving an implementation:

use musli::Decode;

#[derive(Decode)]
#[musli(packed)]
struct MyType {
    data: u8,
}

Implementing manually:

use musli::{Decode, Decoder};

impl<'de, M> Decode<'de, M> for MyType {
    fn decode<D>(cx: &D::Cx, decoder: D) -> Result<Self, D::Error>
    where
        D: Decoder<'de>,
    {
        Ok(Self {
            data: decoder.decode_u8()?,
        })
    }
}

fn decode_u16(self) -> Result<u16, <Self::Cx as Context>::Error>

Decode a 16-bit unsigned integer.

Examples

Deriving an implementation:

use musli::Decode;

#[derive(Decode)]
#[musli(packed)]
struct MyType {
    data: u16,
}

Implementing manually:

use musli::{Decode, Decoder};

impl<'de, M> Decode<'de, M> for MyType {
    fn decode<D>(cx: &D::Cx, decoder: D) -> Result<Self, D::Error>
    where
        D: Decoder<'de>,
    {
        Ok(Self {
            data: decoder.decode_u16()?,
        })
    }
}

fn decode_u32(self) -> Result<u32, <Self::Cx as Context>::Error>

Decode a 32-bit unsigned integer.

Examples

Deriving an implementation:

use musli::Decode;

#[derive(Decode)]
#[musli(packed)]
struct MyType {
    data: u32,
}

Implementing manually:

use musli::{Decode, Decoder};

impl<'de, M> Decode<'de, M> for MyType {
    fn decode<D>(cx: &D::Cx, decoder: D) -> Result<Self, D::Error>
    where
        D: Decoder<'de>,
    {
        Ok(Self {
            data: decoder.decode_u32()?,
        })
    }
}

fn decode_u64(self) -> Result<u64, <Self::Cx as Context>::Error>

Decode a 64-bit unsigned integer.

Examples

Deriving an implementation:

use musli::Decode;

#[derive(Decode)]
#[musli(packed)]
struct MyType {
    data: u64,
}

Implementing manually:

use musli::{Decode, Decoder};

impl<'de, M> Decode<'de, M> for MyType {
    fn decode<D>(cx: &D::Cx, decoder: D) -> Result<Self, D::Error>
    where
        D: Decoder<'de>,
    {
        Ok(Self {
            data: decoder.decode_u64()?,
        })
    }
}

fn decode_u128(self) -> Result<u128, <Self::Cx as Context>::Error>

Decode a 128-bit unsigned integer.

Examples

Deriving an implementation:

use musli::Decode;

#[derive(Decode)]
#[musli(packed)]
struct MyType {
    data: u128,
}

Implementing manually:

use musli::{Decode, Decoder};

impl<'de, M> Decode<'de, M> for MyType {
    fn decode<D>(cx: &D::Cx, decoder: D) -> Result<Self, D::Error>
    where
        D: Decoder<'de>,
    {
        Ok(Self {
            data: decoder.decode_u128()?,
        })
    }
}

fn decode_i8(self) -> Result<i8, <Self::Cx as Context>::Error>

Decode a 8-bit signed integer.

Examples

Deriving an implementation:

use musli::Decode;

#[derive(Decode)]
#[musli(packed)]
struct MyType {
    data: i8,
}

Implementing manually:

use musli::{Decode, Decoder};

impl<'de, M> Decode<'de, M> for MyType {
    fn decode<D>(cx: &D::Cx, decoder: D) -> Result<Self, D::Error>
    where
        D: Decoder<'de>,
    {
        Ok(Self {
            data: decoder.decode_i8()?,
        })
    }
}

fn decode_i16(self) -> Result<i16, <Self::Cx as Context>::Error>

Decode a 16-bit signed integer.

Examples

Deriving an implementation:

use musli::Decode;

#[derive(Decode)]
#[musli(packed)]
struct MyType {
    data: i16,
}

Implementing manually:

use musli::{Decode, Decoder};

impl<'de, M> Decode<'de, M> for MyType {
    fn decode<D>(cx: &D::Cx, decoder: D) -> Result<Self, D::Error>
    where
        D: Decoder<'de>,
    {
        Ok(Self {
            data: decoder.decode_i16()?,
        })
    }
}

fn decode_i32(self) -> Result<i32, <Self::Cx as Context>::Error>

Decode a 32-bit signed integer.

Examples

Deriving an implementation:

use musli::Decode;

#[derive(Decode)]
#[musli(packed)]
struct MyType {
    data: i32,
}

Implementing manually:

use musli::{Decode, Decoder};

impl<'de, M> Decode<'de, M> for MyType {
    fn decode<D>(cx: &D::Cx, decoder: D) -> Result<Self, D::Error>
    where
        D: Decoder<'de>,
    {
        Ok(Self {
            data: decoder.decode_i32()?,
        })
    }
}

fn decode_i64(self) -> Result<i64, <Self::Cx as Context>::Error>

Decode a 64-bit signed integer.

Examples

Deriving an implementation:

use musli::Decode;

#[derive(Decode)]
#[musli(packed)]
struct MyType {
    data: i64,
}

Implementing manually:

use musli::{Decode, Decoder};

impl<'de, M> Decode<'de, M> for MyType {
    fn decode<D>(cx: &D::Cx, decoder: D) -> Result<Self, D::Error>
    where
        D: Decoder<'de>,
    {
        Ok(Self {
            data: decoder.decode_i64()?,
        })
    }
}

fn decode_i128(self) -> Result<i128, <Self::Cx as Context>::Error>

Decode a 128-bit signed integer.

Examples

Deriving an implementation:

use musli::Decode;

#[derive(Decode)]
#[musli(packed)]
struct MyType {
    data: i128,
}

Implementing manually:

use musli::{Decode, Decoder};

impl<'de, M> Decode<'de, M> for MyType {
    fn decode<D>(cx: &D::Cx, decoder: D) -> Result<Self, D::Error>
    where
        D: Decoder<'de>,
    {
        Ok(Self {
            data: decoder.decode_i128()?,
        })
    }
}

fn decode_usize(self) -> Result<usize, <Self::Cx as Context>::Error>

Decode a usize.

Examples

Deriving an implementation:

use musli::Decode;

#[derive(Decode)]
#[musli(packed)]
struct MyType {
    data: usize,
}

Implementing manually:

use musli::{Decode, Decoder};

impl<'de, M> Decode<'de, M> for MyType {
    fn decode<D>(cx: &D::Cx, decoder: D) -> Result<Self, D::Error>
    where
        D: Decoder<'de>,
    {
        Ok(Self {
            data: decoder.decode_usize()?,
        })
    }
}

fn decode_isize(self) -> Result<isize, <Self::Cx as Context>::Error>

Decode a isize.

Examples

Deriving an implementation:

use musli::Decode;

#[derive(Decode)]
#[musli(packed)]
struct MyType {
    data: isize,
}

Implementing manually:

use musli::{Decode, Decoder};

impl<'de, M> Decode<'de, M> for MyType {
    fn decode<D>(cx: &D::Cx, decoder: D) -> Result<Self, D::Error>
    where
        D: Decoder<'de>,
    {
        Ok(Self {
            data: decoder.decode_isize()?,
        })
    }
}

fn decode_f32(self) -> Result<f32, <Self::Cx as Context>::Error>

Decode a 32-bit floating point value.

Examples

Deriving an implementation:

use musli::Decode;

#[derive(Decode)]
#[musli(packed)]
struct MyType {
    data: f32,
}

Implementing manually:

use musli::{Decode, Decoder};

impl<'de, M> Decode<'de, M> for MyType {
    fn decode<D>(cx: &D::Cx, decoder: D) -> Result<Self, D::Error>
    where
        D: Decoder<'de>,
    {
        Ok(Self {
            data: decoder.decode_f32()?,
        })
    }
}

fn decode_f64(self) -> Result<f64, <Self::Cx as Context>::Error>

Decode a 64-bit floating point value.

Examples

Deriving an implementation:

use musli::Decode;

#[derive(Decode)]
#[musli(packed)]
struct MyType {
    data: f64,
}

Implementing manually:

use musli::{Decode, Decoder};

impl<'de, M> Decode<'de, M> for MyType {
    fn decode<D>(cx: &D::Cx, decoder: D) -> Result<Self, D::Error>
    where
        D: Decoder<'de>,
    {
        Ok(Self {
            data: decoder.decode_f64()?,
        })
    }
}

fn decode_array<const N: usize>( self, ) -> Result<[u8; N], <Self::Cx as Context>::Error>

Decode a fixed-length array.

Examples

Deriving an implementation:

use musli::Decode;

#[derive(Decode)]
#[musli(packed)]
struct MyType {
    data: [u8; 128],
}

Implementing manually:

use musli::{Decode, Decoder};

impl<'de, M> Decode<'de, M> for MyType {
    fn decode<D>(cx: &D::Cx, decoder: D) -> Result<Self, D::Error>
    where
        D: Decoder<'de>,
    {
        Ok(Self {
            data: decoder.decode_array()?,
        })
    }
}

fn decode_bytes<V>( self, visitor: V, ) -> Result<V::Ok, <Self::Cx as Context>::Error>

where V: UnsizedVisitor<'de, Self::Cx, [u8]>,

Decode a sequence of bytes whos length is encoded in the payload.

Examples

Deriving an implementation:

use musli::Decode;

#[derive(Decode)]
#[musli(packed)]
struct BytesReference<'de> {
    data: &'de [u8],
}

Implementing manually:

use std::fmt;

use musli::{Context, Decode, Decoder};
use musli::de::UnsizedVisitor;

impl<'de, M> Decode<'de, M> for BytesReference<'de> {
    #[inline]
    fn decode<D>(cx: &D::Cx, decoder: D) -> Result<Self, D::Error>
    where
        D: Decoder<'de>,
    {
        struct Visitor;

        impl<'de, C> UnsizedVisitor<'de, C, [u8]> for Visitor
        where
            C: ?Sized + Context,
        {
            type Ok = &'de [u8];

            #[inline]
            fn expecting(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
                write!(f, "a literal byte reference")
            }

            #[inline]
            fn visit_borrowed(self, _: &C, bytes: &'de [u8]) -> Result<Self::Ok, C::Error> {
                Ok(bytes)
            }
        }

        Ok(Self {
            data: decoder.decode_bytes(Visitor)?,
        })
    }
}

fn decode_string<V>( self, visitor: V, ) -> Result<V::Ok, <Self::Cx as Context>::Error>

where V: UnsizedVisitor<'de, Self::Cx, str>,

Decode a string slice from the current decoder.

Examples

Deriving an implementation:

use musli::Decode;

#[derive(Decode)]
#[musli(packed)]
struct StringReference<'de> {
    data: &'de str,
}

Implementing manually:

use std::fmt;

use musli::{Context, Decode, Decoder};
use musli::de::UnsizedVisitor;

impl<'de, M> Decode<'de, M> for StringReference<'de> {
    #[inline]
    fn decode<D>(cx: &D::Cx, decoder: D) -> Result<Self, D::Error>
    where
        D: Decoder<'de>,
    {
        struct Visitor;

        impl<'de, C> UnsizedVisitor<'de, C, str> for Visitor
        where
            C: ?Sized + Context,
        {
            type Ok = &'de str;

            #[inline]
            fn expecting(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
                write!(f, "exact bytes reference")
            }

            #[inline]
            fn visit_borrowed(self, _: &C, bytes: &'de str) -> Result<Self::Ok, C::Error> {
                Ok(bytes)
            }
        }

        Ok(Self {
            data: decoder.decode_string(Visitor)?,
        })
    }
}

fn decode_option( self, ) -> Result<Option<Self::DecodeSome>, <Self::Cx as Context>::Error>

Decode an optional value.

Examples

Deriving an implementation:

use musli::{Context, Decode};

#[derive(Decode)]
struct OptionalField {
    data: Option<String>,
}

Implementing manually:

use musli::{Context, Decode, Decoder};

impl<'de, M> Decode<'de, M> for OptionalField {
    fn decode<D>(cx: &D::Cx, decoder: D) -> Result<Self, D::Error>
    where
        D: Decoder<'de>,
    {
        let data = if let Some(decoder) = decoder.decode_option()? {
            Some(decoder.decode()?)
        } else {
            None
        };

        Ok(Self { data })
    }
}

fn decode_pack<F, O>(self, f: F) -> Result<O, <Self::Cx as Context>::Error>

where F: FnOnce(&mut Self::DecodePack) -> Result<O, <Self::Cx as Context>::Error>,

Construct an unpack that can decode more than one element at a time.

This hints to the format that it should attempt to decode all of the elements in the packed sequence from an as compact format as possible compatible with what’s being returned by Encoder::pack.

Examples

Deriving an implementation:

use musli::Decode;

#[derive(Decode)]
#[musli(packed)]
struct PackedStruct {
    field: u32,
    data: [u8; 128],
}

Implementing manually:

use musli::{Context, Decode, Decoder};
use musli::de::SequenceDecoder;

impl<'de, M> Decode<'de, M> for PackedStruct {
    #[inline]
    fn decode<D>(cx: &D::Cx, decoder: D) -> Result<Self, D::Error>
    where
        D: Decoder<'de>,
    {
        decoder.decode_pack(|pack| Ok(Self {
            field: pack.next()?,
            data: pack.next()?,
        }))
    }
}

fn decode_sequence<F, O>(self, f: F) -> Result<O, <Self::Cx as Context>::Error>

where F: FnOnce(&mut Self::DecodeSequence) -> Result<O, <Self::Cx as Context>::Error>,

Decode a sequence.

Examples

Deriving an implementation:

use musli::Decode;

#[derive(Decode)]
struct VectorField {
    data: Vec<String>,
}

Implementing manually:

use musli::{Context, Decode, Decoder};
use musli::de::SequenceDecoder;

struct VectorField {
    data: Vec<String>,
}

impl<'de, M> Decode<'de, M> for VectorField {
    fn decode<D>(cx: &D::Cx, decoder: D) -> Result<Self, D::Error>
    where
        D: Decoder<'de>,
    {
        decoder.decode_sequence(|seq| {
            let mut data = Vec::new();

            while let Some(decoder) = seq.try_decode_next()? {
                data.push(decoder.decode()?);
            }

            Ok(Self { data })
        })
    }
}

Deriving an implementation for a tuple:

use musli::Decode;

#[derive(Decode)]
struct TupleStruct(String, u32);

Implementing manually:

use musli::{Context, Decode, Decoder};
use musli::de::SequenceDecoder;
use musli::hint::SequenceHint;

impl<'de, M> Decode<'de, M> for TupleStruct {
    fn decode<D>(cx: &D::Cx, decoder: D) -> Result<Self, D::Error>
    where
        D: Decoder<'de>,
    {
        static HINT: SequenceHint = SequenceHint::with_size(2);

        decoder.decode_sequence_hint(&HINT, |tuple| {
            Ok(Self(tuple.next()?, tuple.next()?))
        })
    }
}

fn decode_sequence_hint<F, O>( self, hint: &SequenceHint, f: F, ) -> Result<O, <Self::Cx as Context>::Error>

where F: FnOnce(&mut Self::DecodeSequence) -> Result<O, <Self::Cx as Context>::Error>,

Decode a sequence with a hint indicating its expected characteristics.

Examples

use musli::{Context, Decode, Decoder};
use musli::de::SequenceDecoder;
use musli::hint::SequenceHint;

impl<'de, M> Decode<'de, M> for TupleStruct {
    fn decode<D>(cx: &D::Cx, decoder: D) -> Result<Self, D::Error>
    where
        D: Decoder<'de>,
    {
        static HINT: SequenceHint = SequenceHint::with_size(2);

        decoder.decode_sequence_hint(&HINT, |tuple| {
            Ok(Self(tuple.next()?, tuple.next()?))
        })
    }
}

fn decode_map<F, O>(self, f: F) -> Result<O, <Self::Cx as Context>::Error>

where F: FnOnce(&mut Self::DecodeMap) -> Result<O, <Self::Cx as Context>::Error>,

Decode a map who’s size is not known at compile time.

Examples

use std::collections::HashMap;

use musli::{Decode, Decoder};
use musli::de::{MapDecoder, EntryDecoder};

impl<'de, M> Decode<'de, M> for MapStruct {
    fn decode<D>(cx: &D::Cx, decoder: D) -> Result<Self, D::Error>
    where
        D: Decoder<'de>,
    {
        decoder.decode_map(|map| {
            let mut data = HashMap::with_capacity(map.size_hint().or_default());

            while let Some((key, value)) = map.entry()? {
                data.insert(key, value);
            }

            Ok(Self { data })
        })
    }
}

fn decode_map_hint<F, O>( self, _: &MapHint, f: F, ) -> Result<O, <Self::Cx as Context>::Error>

where F: FnOnce(&mut Self::DecodeMap) -> Result<O, <Self::Cx as Context>::Error>,

Decode a map using a simplified function.

The length of the map must somehow be determined from the underlying format.

Examples

Deriving an implementation from a struct:

use std::collections::HashMap;

use musli::Decode;

#[derive(Decode)]
struct Struct {
    string: String,
    integer: u32,
}

Implementing manually:

use musli::{Context, Decode, Decoder};
use musli::de::{MapDecoder, EntryDecoder};
use musli::hint::MapHint;

struct Struct {
    string: String,
    integer: u32,
}

impl<'de, M> Decode<'de, M> for Struct {
    fn decode<D>(cx: &D::Cx, decoder: D) -> Result<Self, D::Error>
    where
        D: Decoder<'de>,
    {
        static HINT: MapHint = MapHint::with_size(2);

        decoder.decode_map_hint(&HINT, |st| {
            let mut string = None;
            let mut integer = None;

            while let Some(mut field) = st.decode_entry()? {
                // Note: to avoid allocating `decode_string` needs to be used with a visitor.
                let tag = field.decode_key()?.decode::<String>()?;

                match tag.as_str() {
                    "string" => {
                        string = Some(field.decode_value()?.decode()?);
                    }
                    "integer" => {
                        integer = Some(field.decode_value()?.decode()?);
                    }
                    tag => {
                        return Err(cx.invalid_field_tag("Struct", tag));
                    }
                }
            }

            Ok(Self {
                string: string.ok_or_else(|| cx.expected_tag("Struct", "string"))?,
                integer: integer.ok_or_else(|| cx.expected_tag("Struct", "integer"))?,
            })
        })
    }
}

fn decode_map_entries<F, O>( self, f: F, ) -> Result<O, <Self::Cx as Context>::Error>

where F: FnOnce(&mut Self::DecodeMapEntries) -> Result<O, <Self::Cx as Context>::Error>,

Simplified decoding a map of unknown length.

The length of the map must somehow be determined from the underlying format.

fn decode_variant<F, O>(self, f: F) -> Result<O, <Self::Cx as Context>::Error>

where F: FnOnce(&mut Self::DecodeVariant) -> Result<O, <Self::Cx as Context>::Error>,

Decode a variant using a closure.

Examples

use musli::{Context, Decode};
use musli::de::{Decoder, VariantDecoder};

enum Enum {
    Number(u32),
    String(String),
}

impl<'de, M> Decode<'de, M> for Enum {
    fn decode<D>(cx: &D::Cx, decoder: D) -> Result<Self, D::Error>
    where
        D: Decoder<'de>,
    {
        decoder.decode_variant(|variant| {
            let tag = variant.decode_tag()?.decode()?;
            let value = variant.decode_value()?;

            match tag {
                0 => Ok(Self::Number(value.decode()?)),
                1 => Ok(Self::String(value.decode()?)),
                tag => Err(cx.invalid_variant_tag("Enum", &tag)),
            }
        })
    }
}

fn decode_number<V>( self, visitor: V, ) -> Result<V::Ok, <Self::Cx as Context>::Error>

where V: Visitor<'de, Self::Cx>,

Decode an unknown number using a visitor.

fn decode_any<V>( self, visitor: V, ) -> Result<V::Ok, <Self::Cx as Context>::Error>

where V: Visitor<'de, Self::Cx>,

Decode dynamically through a Visitor.

Dyn Compatibility

This trait is not dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety", so this trait is not object safe.

Implementors