Trait nom_derive::Parse[−][src]

pub trait Parse<I, E = Error<I>> where
    I: InputSlice,
    E: ParseError<I>,
    Self: Sized, {
    fn parse(i: I) -> IResult<I, Self, E>;

    fn parse_be(i: I) -> IResult<I, Self, E> { ... }

    fn parse_le(i: I) -> IResult<I, Self, E> { ... }
}

Common trait for all parsers in nom-derive

This trait is used to provide parser implementations, usually as generic as possible for the error type. Implementations are provided for common and primitive types. The only required method is parse, but it is advised to implement the parse_be and parse_le methods. Derived code will call one of these methods, depending on the field endianness.

Example

A possible implementation for the type u32 is:

ⓘ
impl<I, E> Parse<I, E> for u32
where
    E: ParseError<I>,
    I: InputSlice,
{
    fn parse(i: I) -> IResult<I, Self, E> { be_u32(i) } // default to big-endian
    fn parse_be(i: I) -> IResult<I, Self, E> { be_u32(i) }
    fn parse_le(i: I) -> IResult<I, Self, E> { le_u32(i) }
}

Generic type parameters and input

Note: I is a generic type that is mostly equivalent to &'a [u8]. It is used to “hide” the lifetime of the input slice &'a [u8] and simplify traits implementation and generation of derived code.

It is possible to implement the Parse trait only for &[u8] if the implementation contains non-generic functions.

For example, the implementation for String is:

ⓘ
impl<'a, E> Parse<&'a [u8], E> for String
where
    E: ParseError<&'a [u8]> + FromExternalError<&'a [u8], std::str::Utf8Error>,
{
    fn parse(i: &'a [u8]) -> IResult<&'a [u8], Self, E> {
        let (rem, sz) = <u32>::parse(i)?;
        let (rem, s) = map_res(take(sz as usize), std::str::from_utf8)(rem)?;
        Ok((rem, s.to_owned()))
    }
}

Implementing primitives or specific types

To implement an existing type differently, or a type where implementation was not provided, a common way is to use a newtype pattern:

use nom_derive::{Parse, nom};

use nom::IResult;
use nom::bytes::complete::take;
use nom::combinator::map_res;
use nom::error::{Error, FromExternalError, ParseError};

pub struct MyString(pub String);
impl<'a, E> Parse<&'a [u8], E> for MyString
where
    E: ParseError<&'a [u8]> + FromExternalError<&'a [u8], std::str::Utf8Error>,
{
    fn parse(i: &'a [u8]) -> IResult<&'a [u8], Self, E> {
        let (rem, sz) = <u32>::parse(i)?;
        let (rem, s) = map_res(take(sz as usize), std::str::from_utf8)(rem)?;
        Ok((rem, MyString(s.to_owned())))
    }
}

// error type cannot be inferred by compiler and must be explicit
let res: IResult<_, _, Error<_>> = MyString::parse(input);

Required methods

fn parse(i: I) -> IResult<I, Self, E>[src]

Parse input, not knowing the endianness

Usually, this means choosing between big and little-endian. Default implementations for common types are big-endian.

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Provided methods

fn parse_be(i: I) -> IResult<I, Self, E>[src]

Parse input as Big-Endian

fn parse_le(i: I) -> IResult<I, Self, E>[src]

Parse input as Little-Endian

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Implementations on Foreign Types

impl<I, E> Parse<I, E> for i8 where
    E: ParseError<I>,
    I: InputSlice, [src]

impl<I, E> Parse<I, E> for i16 where
    E: ParseError<I>,
    I: InputSlice, [src]

impl<I, E> Parse<I, E> for i32 where
    E: ParseError<I>,
    I: InputSlice, [src]

impl<I, E> Parse<I, E> for i64 where
    E: ParseError<I>,
    I: InputSlice, [src]

impl<I, E> Parse<I, E> for i128 where
    E: ParseError<I>,
    I: InputSlice, [src]

impl<I, E> Parse<I, E> for u8 where
    E: ParseError<I>,
    I: InputSlice, [src]

impl<I, E> Parse<I, E> for u16 where
    E: ParseError<I>,
    I: InputSlice, [src]

impl<I, E> Parse<I, E> for u32 where
    E: ParseError<I>,
    I: InputSlice, [src]

impl<I, E> Parse<I, E> for u64 where
    E: ParseError<I>,
    I: InputSlice, [src]

impl<I, E> Parse<I, E> for u128 where
    E: ParseError<I>,
    I: InputSlice, [src]

impl<I, E> Parse<I, E> for f32 where
    E: ParseError<I>,
    I: InputSlice, [src]

impl<I, E> Parse<I, E> for f64 where
    E: ParseError<I>,
    I: InputSlice, [src]

impl<'a, E> Parse<&'a [u8], E> for String where
    E: ParseError<&'a [u8]> + FromExternalError<&'a [u8], Utf8Error>, [src]

impl<T, I, E> Parse<I, E> for Option<T> where
    I: Clone + InputSlice,
    E: ParseError<I>,
    T: Parse<I, E>, [src]

impl<T, I, E> Parse<I, E> for Vec<T> where
    I: Clone + PartialEq + InputSlice,
    E: ParseError<I>,
    T: Parse<I, E>, [src]

impl<T1, T2, I, E> Parse<I, E> for (T1, T2) where
    I: Clone + PartialEq + InputSlice,
    E: ParseError<I>,
    T1: Parse<I, E>,
    T2: Parse<I, E>, [src]

impl<T, I, E, const N: usize> Parse<I, E> for [T; N] where
    I: Clone + PartialEq + InputSlice,
    E: ParseError<I> + FromExternalError<I, Vec<T>>,
    T: Parse<I, E>, [src]

Note: this implementation uses const generics and requires rust >= 1.51

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Implementors

impl<L, I, E> Parse<I, E> for LengthData<L, I> where
    I: Clone + PartialEq + InputSlice,
    E: ParseError<I>,
    L: Parse<I, E> + ToUsize, [src]

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