DisplayFromStr for f64 does not appear to work

[jmcph4]

It's quite possible I'm missing something relatively simple but I believe I'm following the documentation correctly.

This code:

use chrono::{DateTime, Utc};
use serde::Deserialize;
use serde_with::serde_as;

pub const JSON: &str = r#"
    {
        "market": "LINK-USD",
        "rate": "0.0000111465",
        "price": "14.7109999997",
        "effectiveAt": "2024-01-29T04:00:00.000Z"
    }
"#;

#[derive(Clone, Debug, Deserialize)]
#[serde_as]
pub struct Foo {
    pub market: String,
    #[serde_as(as = "DisplayFromStr")]
    pub rate: f64,
    #[serde_as(as = "DisplayFromStr")]
    pub price: f64,
    pub effective_at: DateTime<Utc>,
}

fn main() {
    let obj: Result<Foo, serde_json::Error> = serde_json::from_str(&JSON);
    dbg!(&obj);
}

With these dependencies:

[package]
name = "fundser"
version = "0.1.0"
edition = "2021"

# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

[dependencies]
chrono = { version = "0.4.33", features = ["serde"] }
serde = "1.0.196"
serde_json = "1.0.113"
serde_with = { version = "3.5.1", features = ["macros", "json"] }

Results in:

$ cargo run
[src/main.rs:27] &obj = Err(
    Error("invalid type: string \"0.0000111465\", expected f64", line: 4, column: 30),
)

Despite f64 implementing FromStr. Is there something I'm missing?

[jonasbb]

The macro order in Rust is semantically important. The #[serde_as] must come before the #[derive(...)].

#[serde_as]
#[derive(Clone, Debug, Deserialize)]