     1
     2
     3
     4
     5
     6
     7
     8
     9
    10
    11
    12
    13
    14
    15
    16
    17
    18
    19
    20
    21
    22
    23
    24
    25
    26
    27
    28
    29
    30
    31
    32
    33
    34
    35
    36
    37
    38
    39
    40
    41
    42
    43
    44
    45
    46
    47
    48
    49
    50
    51
    52
    53
    54
    55
    56
    57
    58
    59
    60
    61
    62

    //! Structured data associated with `Span`s and `Event`s.
    pub use tracing_core::field::*;

    use crate::Metadata;

    /// Trait implemented to allow a type to be used as a field key.
    ///
    /// <div class="information">
    ///     <div class="tooltip ignore" style="">ⓘ<span class="tooltiptext">Note</span></div>
    /// </div>
    /// <div class="example-wrap" style="display:inline-block">
    /// <pre class="ignore" style="white-space:normal;font:inherit;">
    /// <strong>Note</strong>: Although this is implemented for both the
    /// <a href="./struct.Field.html"><code>Field</code></a> type <em>and</em> any
    /// type that can be borrowed as an <code>&str</code>, only <code>Field</code>
    /// allows <em>O</em>(1) access.
    /// Indexing a field with a string results in an iterative search that performs
    /// string comparisons. Thus, if possible, once the key for a field is known, it
    /// should be used whenever possible.
    /// </pre>
    pub trait AsField: crate::sealed::Sealed {
        /// Attempts to convert `&self` into a `Field` with the specified `metadata`.
        ///
        /// If `metadata` defines this field, then the field is returned. Otherwise,
        /// this returns `None`.
        fn as_field(&self, metadata: &Metadata<'_>) -> Option<Field>;
    }

    // ===== impl AsField =====

    impl AsField for Field {
        #[inline]
        fn as_field(&self, metadata: &Metadata<'_>) -> Option<Field> {
            if self.callsite() == metadata.callsite() {
                Some(self.clone())
            } else {
                None
            }
        }
    }

    impl<'a> AsField for &'a Field {
        #[inline]
        fn as_field(&self, metadata: &Metadata<'_>) -> Option<Field> {
            if self.callsite() == metadata.callsite() {
                Some((*self).clone())
            } else {
                None
            }
        }
    }

    impl AsField for str {
        #[inline]
        fn as_field(&self, metadata: &Metadata<'_>) -> Option<Field> {
            metadata.fields().field(&self)
        }
    }

    impl crate::sealed::Sealed for Field {}
    impl<'a> crate::sealed::Sealed for &'a Field {}
    impl crate::sealed::Sealed for str {}