Enum ExplicitOrAuto 

pub(crate) enum ExplicitOrAuto<T>
where
    T: NotAutoValue,
{
    Auto,
    Explicit(T),
}

A serializable value, or auto.

Used for implementing configuration options that can be explicitly initialized with a placeholder for their “default” value using the Auto variant.

Unlike #[serde(default)] field: T or #[serde(default)] field: Option<T>, fields of this type can be present in the serialized configuration without being assigned a concrete value.

Important: the underlying type must implement [NotAutoValue]. This trait should be implemented using the [impl_not_auto_value], and only for types that do not serialize to the same value as the Auto variant.

Example

In the following serialized TOML config

 foo = "auto"

foo is set to Auto, which indicates the implementation should use a default (but not necessarily Default::default) value for the foo option.

For example, f field foo defaults to 13 if feature bar is enabled, and 9000 otherwise, a configuration with foo set to "auto" will behave in the “default” way regardless of which features are enabled.

struct Foo(usize);

impl Default for Foo {
    fn default() -> Foo {
        if cfg!(feature = "bar") {
            Foo(13)
        } else {
            Foo(9000)
        }
    }
}

impl Foo {
    fn from_explicit_or_auto(foo: ExplicitOrAuto<Foo>) -> Self {
        match foo {
            // If Auto, choose a sensible default for foo
            ExplicitOrAuto::Auto => Default::default(),
            ExplicitOrAuto::Foo(foo) => foo,
        }
    }
}

struct Config {
   foo: ExplicitOrAuto<Foo>,
}

Variants

Auto

Automatic

Explicit(T)

Explicitly specified

Implementations

impl<T> ExplicitOrAuto<T>

where T: NotAutoValue,

pub fn into_value(self) -> Option<T>

Returns the explicitly set value, or None.

use tor_config::ExplicitOrAuto;

fn calculate_default() -> usize { //...
let explicit_or_auto: ExplicitOrAuto<usize> = // ...
let _: usize = explicit_or_auto.into_value().unwrap_or_else(|| calculate_default());

pub fn as_value(&self) -> Option<&T>

Returns a reference to the explicitly set value, or None.

Like ExplicitOrAuto::into_value, except it returns a reference to the inner type.

pub fn map<U>(self, f: impl FnOnce(T) -> U) -> ExplicitOrAuto<U>

where U: NotAutoValue,

Maps an ExplicitOrAuto<T> to an ExplicitOrAuto<U> by applying a function to a contained value.

Trait Implementations

impl<T> Clone for ExplicitOrAuto<T>

where T: Clone + NotAutoValue,

fn clone(&self) -> ExplicitOrAuto<T>

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl<T> Debug for ExplicitOrAuto<T>

where T: Debug + NotAutoValue,

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

Formats the value using the given formatter.

impl<T> Default for ExplicitOrAuto<T>

where T: NotAutoValue,

fn default() -> ExplicitOrAuto<T>

Returns the “default value” for a type.

impl<'de, T> Deserialize<'de> for ExplicitOrAuto<T>

where T: NotAutoValue + Deserialize<'de>,

fn deserialize<__D>( __deserializer: __D, ) -> Result<ExplicitOrAuto<T>, <__D as Deserializer<'de>>::Error>

where __D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl<T> From<T> for ExplicitOrAuto<T>

where T: NotAutoValue,

fn from(x: T) -> ExplicitOrAuto<T>

Converts to this type from the input type.

impl<T> Hash for ExplicitOrAuto<T>

where T: Hash + NotAutoValue,

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

where __H: Hasher,

Feeds this value into the given Hasher.

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

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl<T> Ord for ExplicitOrAuto<T>

where T: Ord + NotAutoValue,

fn cmp(&self, other: &ExplicitOrAuto<T>) -> Ordering

This method returns an Ordering between self and other.

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

where Self: Sized,

Compares and returns the maximum of two values.

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

where Self: Sized,

Compares and returns the minimum of two values.

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

where Self: Sized,

Restrict a value to a certain interval.

impl<T> PartialEq for ExplicitOrAuto<T>

where T: PartialEq + NotAutoValue,

fn eq(&self, other: &ExplicitOrAuto<T>) -> bool

Tests for self and other values to be equal, and is used by ==.

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

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl<T> PartialOrd for ExplicitOrAuto<T>

where T: PartialOrd + NotAutoValue,

fn partial_cmp(&self, other: &ExplicitOrAuto<T>) -> Option<Ordering>

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

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

Tests less than (for self and other) and is used by the < operator.

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

Tests less than or equal to (for self and other) and is used by the <= operator.

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

Tests greater than (for self and other) and is used by the > operator.

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

Tests greater than or equal to (for self and other) and is used by the >= operator.

impl<T> Serialize for ExplicitOrAuto<T>

where T: NotAutoValue + Serialize,

fn serialize<__S>( &self, __serializer: __S, ) -> Result<<__S as Serializer>::Ok, <__S as Serializer>::Error>

where __S: Serializer,

Serialize this value into the given Serde serializer.

impl<T> Copy for ExplicitOrAuto<T>

where T: Copy + NotAutoValue,

impl<T> Eq for ExplicitOrAuto<T>

where T: Eq + NotAutoValue,

impl<T> StructuralPartialEq for ExplicitOrAuto<T>

where T: NotAutoValue,