Struct log::kv::Value

source ·

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

Expand description

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.

Struct log::kv::Value

§Capturing values

§Using the Value::from_* methods

§Using the ToValue trait

§Using the standard From trait

§Data model

§Serialization

Implementations§

impl<'v> Value<'v>

pub fn to_cow_str(&self) -> Option<Cow<'v, str>>

impl<'v> Value<'v>

pub fn from_any<T>(value: &'v T) -> Selfwhere T: ToValue,

pub fn from_debug<T>(value: &'v T) -> Selfwhere T: Debug,

pub fn from_display<T>(value: &'v T) -> Selfwhere T: Display,

pub fn from_serde<T>(value: &'v T) -> Selfwhere T: Serialize,

pub fn from_sval<T>(value: &'v T) -> Selfwhere T: Value,

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

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

pub fn from_dyn_error(err: &'v (dyn Error + 'static)) -> Self

pub fn null() -> Self

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

impl<'v> Value<'v>

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

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

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

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

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

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

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

impl<'v> Value<'v>

pub fn to_borrowed_error(&self) -> Option<&(dyn Error + 'static)>

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

Trait Implementations§

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

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

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

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

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

fn from(value: &'v NonZeroI128) -> Self

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

fn from(value: &'v NonZeroI16) -> Self

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

fn from(value: &'v NonZeroI32) -> Self

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

fn from(value: &'v NonZeroI64) -> Self

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

fn from(value: &'v NonZeroI8) -> Self

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

fn from(value: &'v NonZeroIsize) -> Self

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

fn from(value: &'v NonZeroU128) -> Self

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

fn from(value: &'v NonZeroU16) -> Self

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

fn from(value: &'v NonZeroU32) -> Self

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

fn from(value: &'v NonZeroU64) -> Self

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

fn from(value: &'v NonZeroU8) -> Self

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

fn from(value: &'v NonZeroUsize) -> Self

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

fn from(v: &'v String) -> Self

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

§Using the `Value::from_*` methods

§Using the `ToValue` trait

§Using the standard `From` trait

pub fn from_any<T>(value: &'v T) -> Self
where T: ToValue,

pub fn from_debug<T>(value: &'v T) -> Self
where T: Debug,

pub fn from_display<T>(value: &'v T) -> Self
where T: Display,

pub fn from_serde<T>(value: &'v T) -> Self
where T: Serialize,

pub fn from_sval<T>(value: &'v T) -> Self
where T: Value,