# Metadata in log - Rust
Metadata about a log message.
Keywords: rust, rustlang, rust-lang, Metadata

# Struct log::Metadata

source · [−]

    pub struct Metadata<'a> { /* private fields */ }

Expand description

Metadata about a log message.

## Use

`Metadata` structs are created when users of the library use logging macros.

They are consumed by implementations of the `Log` trait in the `enabled` method.

`Record`s use `Metadata` to determine the log message’s severity and target.

Users should use the `log_enabled!` macro in their code to avoid constructing expensive log messages.

## Examples

ⓘ

    use log::{Record, Level, Metadata};

    struct MyLogger;

    impl log::Log for MyLogger {
        fn enabled(&self, metadata: &Metadata) -> bool {
            metadata.level() <= Level::Info
        }

        fn log(&self, record: &Record) {
            if self.enabled(record.metadata()) {
                println!("{} - {}", record.level(), record.args());
            }
        }
        fn flush(&self) {}
    }

## Implementations

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### impl<'a> Metadata<'a>

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#### pub fn builder() -> MetadataBuilder<'a>

Returns a new builder.

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#### pub fn level(&self) -> Level

The verbosity level of the message.

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#### pub fn target(&self) -> &'a str

The name of the target of the directive.

## Trait Implementations

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### impl<'a> Clone for Metadata<'a>

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#### fn clone(&self) -> Metadata<'a>

Returns a copy of the value. Read more

1.0.0 · source

#### fn clone_from(&mut self, source: &Self)

Performs copy-assignment from `source`. Read more

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### impl<'a> Debug for Metadata<'a>

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#### fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter. Read more

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### impl<'a> Hash for Metadata<'a>

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#### fn hash<__H: Hasher>(&self, state: &mut __H)

Feeds this value into the given `Hasher`. Read more

1.3.0 · source

#### fn hash_slice<H>(data: &[Self], state: &mut H) where
H: Hasher,

Feeds a slice of this type into the given `Hasher`. Read more

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### impl<'a> Ord for Metadata<'a>

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#### fn cmp(&self, other: &Metadata<'a>) -> Ordering

This method returns an `Ordering` between `self` and `other`. Read more

1.21.0 · source

#### fn max(self, other: Self) -> Self

Compares and returns the maximum of two values. Read more

1.21.0 · source

#### fn min(self, other: Self) -> Self

Compares and returns the minimum of two values. Read more

1.50.0 · source

#### fn clamp(self, min: Self, max: Self) -> Self

Restrict a value to a certain interval. Read more

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### impl<'a> PartialEq<Metadata<'a>> for Metadata<'a>

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#### fn eq(&self, other: &Metadata<'a>) -> bool

This method tests for `self` and `other` values to be equal, and is used by `==`. Read more

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#### fn ne(&self, other: &Metadata<'a>) -> bool

This method tests for `!=`.

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### impl<'a> PartialOrd<Metadata<'a>> for Metadata<'a>

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#### fn partial_cmp(&self, other: &Metadata<'a>) -> Option<Ordering>

This method returns an ordering between `self` and `other` values if one exists. Read more

1.0.0 · source

#### fn lt(&self, other: &Rhs) -> bool

This method tests less than (for `self` and `other`) and is used by the `<` operator. Read more

1.0.0 · source

#### fn le(&self, other: &Rhs) -> bool

This method tests less than or equal to (for `self` and `other`) and is used by the `<=` operator. Read more

1.0.0 · source

#### fn gt(&self, other: &Rhs) -> bool

This method tests greater than (for `self` and `other`) and is used by the `>` operator. Read more

1.0.0 · source

#### fn ge(&self, other: &Rhs) -> bool

This method tests greater than or equal to (for `self` and `other`) and is used by the `>=` operator. Read more

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### impl<'a> Eq for Metadata<'a>

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### impl<'a> StructuralEq for Metadata<'a>

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### impl<'a> StructuralPartialEq for Metadata<'a>

## Auto Trait Implementations

### impl<'a> RefUnwindSafe for Metadata<'a>

### impl<'a> Send for Metadata<'a>

### impl<'a> Sync for Metadata<'a>

### impl<'a> Unpin for Metadata<'a>

### impl<'a> UnwindSafe for Metadata<'a>

## Blanket Implementations

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### impl<T> Any for T where
T: 'static + ?Sized,

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#### fn type_id(&self) -> TypeId

Gets the `TypeId` of `self`. Read more

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### impl<T> Borrow<T> for T where
T: ?Sized,

const: unstable · source

#### fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more

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### impl<T> BorrowMut<T> for T where
T: ?Sized,

const: unstable · source

#### fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more

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### impl<T> From<T> for T

const: unstable · source

#### fn from(t: T) -> T

Returns the argument unchanged.

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### impl<T, U> Into<U> for T where
U: From<T>,

const: unstable · source

#### fn into(self) -> U

Calls `U::from(self)`.

That is, this conversion is whatever the implementation of `From<T> for U` chooses to do.

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### impl<T, U> TryFrom<U> for T where
U: Into<T>,

#### type Error = Infallible

The type returned in the event of a conversion error.

const: unstable · source

#### fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.

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### impl<T, U> TryInto<U> for T where
U: TryFrom<T>,

#### type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.

const: unstable · source

#### fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.