Struct serde_str_helpers::DeserBorrowStr

pub struct DeserBorrowStr<'a>(_);

This is a helper for deserializing using TryFrom more efficiently.

When using #[serde(try_from = "String"] when deserializing a value that doesn't neet to hold the string (e.g. an integer value) serde would allocate the string even if it doesn't have to.

A naive idea is to use std::borrow::Cow to solve it. Sadly, the implementation of Deserialize for Cow<'de, str> doesn't borrow the string, so it still allocates needlessly. This helper solves the issue.

Our DeserBorrowStr is written such that it borrows the str when possible, avoiding the allocation. It may still need to allocate, for example if string decoding (unescaping) has to be performed.

Example

use serde_derive::Deserialize;
use serde_str_helpers::DeserBorrowStr;
use core::convert::TryFrom;

#[derive(Deserialize)]
#[serde(try_from = "DeserBorrowStr")]
struct StringlyNumber(u64);

impl<'a> TryFrom<DeserBorrowStr<'a>> for StringlyNumber {
    type Error = core::num::ParseIntError;

    fn try_from(value: DeserBorrowStr<'a>) -> Result<Self, Self::Error> {
        value.parse().map(StringlyNumber)
    }
}

let x = serde_json::from_str::<StringlyNumber>("\"42\"").expect("Failed to deserialize");

assert_eq!(x.0, 42);

Trait Implementations

impl<'a> AsRef<str> for DeserBorrowStr<'a>

pub fn as_ref(&self) -> &str

Performs the conversion.

impl<'a> Borrow<str> for DeserBorrowStr<'a>

pub fn borrow(&self) -> &str

Immutably borrows from an owned value.

impl<'a> Deref for DeserBorrowStr<'a>

type Target = str

The resulting type after dereferencing.

pub fn deref(&self) -> &Self::Target

Dereferences the value.

impl<'de: 'a, 'a> Deserialize<'de> for DeserBorrowStr<'a>

pub fn deserialize<__D>(__deserializer: __D) -> Result<Self, __D::Error> where
    __D: Deserializer<'de>, 

Deserialize this value from the given Serde deserializer.

impl<'a> From<Cow<'a, str>> for DeserBorrowStr<'a>

pub fn from(value: Cow<'a, str>) -> Self

Performs the conversion.

impl<'a> From<DeserBorrowStr<'a>> for Cow<'a, str>

pub fn from(value: DeserBorrowStr<'a>) -> Self

Performs the conversion.

impl<'a> From<DeserBorrowStr<'a>> for String

pub fn from(value: DeserBorrowStr<'a>) -> Self

Performs the conversion.