Trait FormatFields

pub trait FormatFields<'writer> {
    // Required method
    fn format_fields<R: RecordFields>(
        &self,
        writer: Writer<'writer>,
        fields: R,
    ) -> Result;

    // Provided method
    fn add_fields(
        &self,
        current: &'writer mut FormattedFields<Self>,
        fields: &Record<'_>,
    ) -> Result { ... }
}

Available on crate features fmt and std only.

A type that can format a set of fields to a Writer.

FormatFields is primarily used in the context of FmtSubscriber. Each time a span or event with fields is recorded, the subscriber will format those fields with its associated FormatFields implementation.

Required Methods

fn format_fields<R: RecordFields>( &self, writer: Writer<'writer>, fields: R, ) -> Result

Format the provided fields to the provided Writer, returning a result.

Provided Methods

fn add_fields( &self, current: &'writer mut FormattedFields<Self>, fields: &Record<'_>, ) -> Result

Record additional field(s) on an existing span.

By default, this appends a space to the current set of fields if it is non-empty, and then calls self.format_fields. If different behavior is required, the default implementation of this method can be overridden.

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

impl<'a> FormatFields<'a> for JsonFields

impl<'writer> FormatFields<'writer> for Pretty

impl<'writer, M> FormatFields<'writer> for M

where M: MakeOutput<Writer<'writer>, Result>, M::Visitor: VisitFmt + VisitOutput<Result>,

impl<'writer, S, N> FormatFields<'writer> for FmtContext<'_, S, N>

where S: Subscriber + for<'lookup> LookupSpan<'lookup>, N: FormatFields<'writer> + 'static,