Struct mz_persist_client::dyn_cfg::Config

pub struct Config<T: ConfigType> {
    name: &'static str,
    desc: &'static str,
    default: T::Default,
}

A handle to a dynamically updatable configuration value.

This represents a strongly-typed named config of type T. It may be registered to a set of such configs with ConfigSet::add and then later used to retrieve the latest value at any time with Self::get.

The supported types are bool, usize, and String.

TODO(cfg): Add Duration in a followup.

Fields

name: &'static str

desc: &'static str

default: T::Default

Implementations

impl<T: ConfigType> Config<T>

pub const fn new( name: &'static str, default: T::Default, desc: &'static str ) -> Self

Constructs a handle for a config of type T.

It is best practice, but not strictly required, for the name to be globally unique within a process.

TODO(cfg): Add some sort of categorization of config purpose here: e.g. limited-lifetime rollout flag, CYA, magic number that we never expect to tune, magic number that we DO expect to tune, etc. This could be used to power something like a --future-default-flags for CI, to replace part or all of the manually maintained list.

TODO(cfg): See if we can make this more Rust-y and take these params as a struct (the obvious thing hits some issues with const combined with Drop).

pub fn name(&self) -> &str

The name of this config.

pub fn desc(&self) -> &str

The description of this config.

pub fn default(&self) -> &T::Default

The default value of this config.

pub fn register(&self, set: &mut ConfigSet) -> T

Adds this config to the given set.

Names are required to be unique within a set, but each set is entirely independent. The same Config may be registered to multiple ConfigSets and thus have independent values (e.g. imagine a units test executing concurrently in the same process).

Panics if a config with the same name has previously been registered to this set.

pub fn get(&self, set: &ConfigSet) -> T

Returns the latest value of this config within the given set.

Panics if this config was not previously registered to the set.

TODO(cfg): Decide if this should be a method on ConfigSet instead to match the precedent of BTreeMap/HashMap::get taking a key. It’s like this initially because it was thought that the Config definition was the more important “noun” and also that rustfmt would maybe work better on this ordering.

pub fn shared(&self, set: &ConfigSet) -> Arc<T::Shared>

Returns the shared value of this config in the given set.

This allows users to amortize the name lookup with Self::get_from_shared.

pub fn get_from_shared(&self, shared: &T::Shared) -> T

Self::get except from a previously looked up shared value returned by Self::shared.

Trait Implementations

impl<T: Clone + ConfigType> Clone for Config<T>where T::Default: Clone,

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

Returns a copy of the value.

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

Performs copy-assignment from source.

impl<T: Debug + ConfigType> Debug for Config<T>where T::Default: Debug,

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

Formats the value using the given formatter.