Struct Value 

pub struct Value<'v> { /* private fields */ }

A value in a key-value.

Values are an anonymous bag containing some structured datum.

Capturing values

There are a few ways to capture a value:

• Using the Value::from_* methods.
• Using the ToValue trait.
• Using the standard From trait.

Using the Value::from_* methods

Value offers a few constructor methods that capture values of different kinds.

use log::kv::Value;

let value = Value::from_debug(&42i32);

assert_eq!(None, value.to_i64());

Using the ToValue trait

The ToValue trait can be used to capture values generically. It’s the bound used by Source.

let value = 42i32.to_value();

assert_eq!(Some(42), value.to_i64());

Using the standard From trait

Standard types that implement ToValue also implement From.

use log::kv::Value;

let value = Value::from(42i32);

assert_eq!(Some(42), value.to_i64());

Data model

Values can hold one of a number of types:

• Null: The absence of any other meaningful value. Note that Some(Value::null()) is not the same as None. The former is null while the latter is undefined. This is important to be able to tell the difference between a key-value that was logged, but its value was empty (Some(Value::null())) and a key-value that was never logged at all (None).
• Strings: str, char.
• Booleans: bool.
• Integers: u8-u128, i8-i128, NonZero*.
• Floating point numbers: f32-f64.
• Errors: dyn (Error + 'static).
• serde: Any type in serde’s data model.
• sval: Any type in sval’s data model.

Serialization

Values provide a number of ways to be serialized.

For basic types the Value::visit method can be used to extract the underlying typed value. However, this is limited in the amount of types supported (see the VisitValue trait methods).

For more complex types one of the following traits can be used:

• sval::Value, requires the kv_sval feature.
• serde::Serialize, requires the kv_serde feature.

You don’t need a visitor to serialize values through serde or sval.

A value can always be serialized using any supported framework, regardless of how it was captured. If, for example, a value was captured using its Display implementation, it will serialize through serde as a string. If it was captured as a struct using serde, it will also serialize as a struct through sval, or can be formatted using a Debug-compatible representation.

Implementations

impl<'v> Value<'v>

pub fn from_any<T>(value: &'v T) -> Value<'v>

where T: ToValue,

Get a value from a type implementing ToValue.

pub fn from_debug<T>(value: &'v T) -> Value<'v>

where T: Debug,

Get a value from a type implementing std::fmt::Debug.

pub fn from_display<T>(value: &'v T) -> Value<'v>

where T: Display,

Get a value from a type implementing std::fmt::Display.

pub fn from_dyn_debug(value: &'v dyn Debug) -> Value<'v>

Get a value from a dynamic std::fmt::Debug.

pub fn from_dyn_display(value: &'v dyn Display) -> Value<'v>

Get a value from a dynamic std::fmt::Display.

pub fn null() -> Value<'v>

Get a null value.

pub fn visit(&self, visitor: impl VisitValue<'v>) -> Result<(), Error>

Inspect this value using a simple visitor.

When the kv_serde or kv_sval features are enabled, you can also serialize a value using its Serialize or Value implementation.

impl<'v> Value<'v>

pub fn to_u64(&self) -> Option<u64>

Try convert this value into a u64.

pub fn to_i64(&self) -> Option<i64>

Try convert this value into a i64.

pub fn to_u128(&self) -> Option<u128>

Try convert this value into a u128.

pub fn to_i128(&self) -> Option<i128>

Try convert this value into a i128.

pub fn to_f64(&self) -> Option<f64>

Try convert this value into a f64.

pub fn to_char(&self) -> Option<char>

Try convert this value into a char.

pub fn to_bool(&self) -> Option<bool>

Try convert this value into a bool.

impl<'v> Value<'v>

pub fn to_borrowed_str(&self) -> Option<&'v str>

Try to convert this value into a borrowed string.

Trait Implementations

impl<'v> Clone for Value<'v>

fn clone(&self) -> Value<'v>

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl<'v> Debug for Value<'v>

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

Formats the value using the given formatter.

impl<'v> Display for Value<'v>

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

Formats the value using the given formatter.

impl<'v> From<&'v NonZero<i128>> for Value<'v>

fn from(value: &'v NonZero<i128>) -> Value<'v>

Converts to this type from the input type.

impl<'v> From<&'v NonZero<i16>> for Value<'v>

fn from(value: &'v NonZero<i16>) -> Value<'v>

Converts to this type from the input type.

impl<'v> From<&'v NonZero<i32>> for Value<'v>

fn from(value: &'v NonZero<i32>) -> Value<'v>

Converts to this type from the input type.

impl<'v> From<&'v NonZero<i64>> for Value<'v>

fn from(value: &'v NonZero<i64>) -> Value<'v>

Converts to this type from the input type.

impl<'v> From<&'v NonZero<i8>> for Value<'v>

fn from(value: &'v NonZero<i8>) -> Value<'v>

Converts to this type from the input type.

impl<'v> From<&'v NonZero<isize>> for Value<'v>

fn from(value: &'v NonZero<isize>) -> Value<'v>

Converts to this type from the input type.

impl<'v> From<&'v NonZero<u128>> for Value<'v>

fn from(value: &'v NonZero<u128>) -> Value<'v>

Converts to this type from the input type.

impl<'v> From<&'v NonZero<u16>> for Value<'v>

fn from(value: &'v NonZero<u16>) -> Value<'v>

Converts to this type from the input type.

impl<'v> From<&'v NonZero<u32>> for Value<'v>

fn from(value: &'v NonZero<u32>) -> Value<'v>

Converts to this type from the input type.

impl<'v> From<&'v NonZero<u64>> for Value<'v>

fn from(value: &'v NonZero<u64>) -> Value<'v>

Converts to this type from the input type.

impl<'v> From<&'v NonZero<u8>> for Value<'v>

fn from(value: &'v NonZero<u8>) -> Value<'v>

Converts to this type from the input type.

impl<'v> From<&'v NonZero<usize>> for Value<'v>

fn from(value: &'v NonZero<usize>) -> Value<'v>

Converts to this type from the input type.

impl<'v> From<&'v bool> for Value<'v>

fn from(value: &'v bool) -> Value<'v>

Converts to this type from the input type.

impl<'v> From<&'v char> for Value<'v>

fn from(value: &'v char) -> Value<'v>

Converts to this type from the input type.

impl<'v> From<&'v f32> for Value<'v>

fn from(value: &'v f32) -> Value<'v>

Converts to this type from the input type.

impl<'v> From<&'v f64> for Value<'v>

fn from(value: &'v f64) -> Value<'v>

Converts to this type from the input type.

impl<'v> From<&'v i128> for Value<'v>

fn from(value: &'v i128) -> Value<'v>

Converts to this type from the input type.

impl<'v> From<&'v i16> for Value<'v>

fn from(value: &'v i16) -> Value<'v>

Converts to this type from the input type.

impl<'v> From<&'v i32> for Value<'v>

fn from(value: &'v i32) -> Value<'v>

Converts to this type from the input type.

impl<'v> From<&'v i64> for Value<'v>

fn from(value: &'v i64) -> Value<'v>

Converts to this type from the input type.

impl<'v> From<&'v i8> for Value<'v>

fn from(value: &'v i8) -> Value<'v>

Converts to this type from the input type.

impl<'v> From<&'v isize> for Value<'v>

fn from(value: &'v isize) -> Value<'v>

Converts to this type from the input type.

impl<'v> From<&'v str> for Value<'v>

fn from(value: &'v str) -> Value<'v>

Converts to this type from the input type.

impl<'v> From<&'v u128> for Value<'v>

fn from(value: &'v u128) -> Value<'v>

Converts to this type from the input type.

impl<'v> From<&'v u16> for Value<'v>

fn from(value: &'v u16) -> Value<'v>

Converts to this type from the input type.

impl<'v> From<&'v u32> for Value<'v>

fn from(value: &'v u32) -> Value<'v>

Converts to this type from the input type.

impl<'v> From<&'v u64> for Value<'v>

fn from(value: &'v u64) -> Value<'v>

Converts to this type from the input type.

impl<'v> From<&'v u8> for Value<'v>

fn from(value: &'v u8) -> Value<'v>

Converts to this type from the input type.

impl<'v> From<&'v usize> for Value<'v>

fn from(value: &'v usize) -> Value<'v>

Converts to this type from the input type.

impl<'v> From<NonZero<i128>> for Value<'v>

fn from(value: NonZero<i128>) -> Value<'v>

Converts to this type from the input type.

impl<'v> From<NonZero<i16>> for Value<'v>

fn from(value: NonZero<i16>) -> Value<'v>

Converts to this type from the input type.

impl<'v> From<NonZero<i32>> for Value<'v>

fn from(value: NonZero<i32>) -> Value<'v>

Converts to this type from the input type.

impl<'v> From<NonZero<i64>> for Value<'v>

fn from(value: NonZero<i64>) -> Value<'v>

Converts to this type from the input type.

impl<'v> From<NonZero<i8>> for Value<'v>

fn from(value: NonZero<i8>) -> Value<'v>

Converts to this type from the input type.

impl<'v> From<NonZero<isize>> for Value<'v>

fn from(value: NonZero<isize>) -> Value<'v>

Converts to this type from the input type.

impl<'v> From<NonZero<u128>> for Value<'v>

fn from(value: NonZero<u128>) -> Value<'v>

Converts to this type from the input type.

impl<'v> From<NonZero<u16>> for Value<'v>

fn from(value: NonZero<u16>) -> Value<'v>

Converts to this type from the input type.

impl<'v> From<NonZero<u32>> for Value<'v>

fn from(value: NonZero<u32>) -> Value<'v>

Converts to this type from the input type.

impl<'v> From<NonZero<u64>> for Value<'v>

fn from(value: NonZero<u64>) -> Value<'v>

Converts to this type from the input type.

impl<'v> From<NonZero<u8>> for Value<'v>

fn from(value: NonZero<u8>) -> Value<'v>

Converts to this type from the input type.

impl<'v> From<NonZero<usize>> for Value<'v>

fn from(value: NonZero<usize>) -> Value<'v>

Converts to this type from the input type.

impl<'v> From<bool> for Value<'v>

fn from(value: bool) -> Value<'v>

Converts to this type from the input type.

impl<'v> From<char> for Value<'v>

fn from(value: char) -> Value<'v>

Converts to this type from the input type.

impl<'v> From<f32> for Value<'v>

fn from(value: f32) -> Value<'v>

Converts to this type from the input type.

impl<'v> From<f64> for Value<'v>

fn from(value: f64) -> Value<'v>

Converts to this type from the input type.

impl<'v> From<i128> for Value<'v>

fn from(value: i128) -> Value<'v>

Converts to this type from the input type.

impl<'v> From<i16> for Value<'v>

fn from(value: i16) -> Value<'v>

Converts to this type from the input type.

impl<'v> From<i32> for Value<'v>

fn from(value: i32) -> Value<'v>

Converts to this type from the input type.

impl<'v> From<i64> for Value<'v>

fn from(value: i64) -> Value<'v>

Converts to this type from the input type.

impl<'v> From<i8> for Value<'v>

fn from(value: i8) -> Value<'v>

Converts to this type from the input type.

impl<'v> From<isize> for Value<'v>

fn from(value: isize) -> Value<'v>

Converts to this type from the input type.

impl<'v> From<u128> for Value<'v>

fn from(value: u128) -> Value<'v>

Converts to this type from the input type.

impl<'v> From<u16> for Value<'v>

fn from(value: u16) -> Value<'v>

Converts to this type from the input type.

impl<'v> From<u32> for Value<'v>

fn from(value: u32) -> Value<'v>

Converts to this type from the input type.

impl<'v> From<u64> for Value<'v>

fn from(value: u64) -> Value<'v>

Converts to this type from the input type.

impl<'v> From<u8> for Value<'v>

fn from(value: u8) -> Value<'v>

Converts to this type from the input type.

impl<'v> From<usize> for Value<'v>

fn from(value: usize) -> Value<'v>

Converts to this type from the input type.

impl<'v> ToValue for Value<'v>

fn to_value(&self) -> Value<'_>

Perform the conversion.