Struct slog::PushFnValue

pub struct PushFnValue<F>(pub F)
 where
    F: 'static + for<'c, 'd> Fn(&'c Record<'d>, PushFnValueSerializer<'c>) -> Result;

Lazy Value that writes to Serializer

It’s more ergonomic for closures used as lazy values to return type implementing Serialize, but sometimes that forces an allocation (eg. Strings)

In some cases it might make sense for another closure form to be used - one taking a serializer as an argument, which avoids lifetimes / allocation issues.

Generally this method should be used if it avoids a big allocation of Serialize-implementing type in performance-critical logging statement.

#[macro_use]
extern crate slog;
use slog::{PushFnValue, Logger, Discard};

fn main() {
    // Create a logger with a key-value printing
    // `file:line` string value for every logging statement.
    // `Discard` `Drain` used for brevity.
    let root = Logger::root(Discard, o!(
        "source_location" => PushFnValue(|record , s| {
             s.serialize(
                  format_args!(
                       "{}:{}",
                       record.file(),
                       record.line(),
                  )
             )
        })
    ));
}

Trait Implementations

impl<F> Value for PushFnValue<F> where
    F: 'static + for<'c, 'd> Fn(&'c Record<'d>, PushFnValueSerializer<'c>) -> Result, 

fn serialize(
    &self,
    record: &Record<'_>,
    key: Key,
    serializer: &mut dyn Serializer
) -> Result

Serialize self into Serializer