Struct gstuff::Constructible

pub struct Constructible<T> { /* fields omitted */ }

A cell that can be initialized, but only once.
Once initialized the cell remains immutable, allowing us to alias the value.

NB: There is a similar abstraction at https://github.com/matklad/once_cell. (I’ve only just discovered it, some months after implementing the Constructible myself).

Implementations

impl<T> Constructible<T>

pub fn initialize<'a>(&'a self, v: Box<T>) -> Result<&'a T, String>

Provides the cell with the value.
The value is effectively pinned in the cell, it won’t be moved.
Returns an error if the cell is already initialized.

pub fn pin<'a>(&'a self, v: T) -> Result<&'a T, String>

Provides the cell with the value.
The value is moved into a Box and pinned there.
Returns an error if the cell is already initialized.

pub fn or<'a, F>(&'a self, default: &'a F) -> &'a T where
    F: Fn() -> &'a T,
    T: 'a, 

Get a reference to the value.
If the value is not (yet) available then returns the reference provided by default.

pub fn copy_or(&self, default: T) -> T where
    T: Copy, 

Returns a copy of the value or the default if the value is not yet available.

pub fn clone_or(&self, default: T) -> T where
    T: Clone, 

Returns a clone of the value or the default if the value is not yet available.

pub fn ok_or<'a, E>(&'a self, error: E) -> Result<&'a T, E>

Returns a reference to the value or the given error if the value is not yet available.

pub fn as_option<'a>(&'a self) -> Option<&'a T>

Returns a reference to the value or None if the value is not yet available.

pub fn is_none(&self) -> bool

True if the value is not yet available.

pub fn is_some(&self) -> bool

True if the cell is now initialized with a value.

pub fn iter<'a>(&'a self) -> IntoIter<&'a T>

Returns a reference to the value unless it was not yet initialized.

Trait Implementations

impl<T> Debug for Constructible<T> where
    T: Debug, 

Debug formatting similar to Option<&T>.

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

Formats the value using the given formatter.

impl<T> Default for Constructible<T>

Creates a cell without a value.
Use pin or initialize to provide the value later.

fn default() -> Constructible<T>

Returns the “default value” for a type.

impl<T> Display for Constructible<T> where
    T: Display, 

Prints the value or “-” if it is not yet available.

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

Formats the value using the given formatter.

impl<T> Drop for Constructible<T>

fn drop(&mut self)

Executes the destructor for this type.

impl<T> From<Option<T>> for Constructible<T>

Translate an Option into a Constructible cell.
If the Option has a value then the cell with be initialized with it.
If the Option is empty then the cell will be empty as well, and waiting for delayed initialization.

fn from(v: Option<T>) -> Constructible<T>

Performs the conversion.

impl<T> From<T> for Constructible<T>

Pre-initialize the cell with the given value.

fn from(v: T) -> Constructible<T>

Performs the conversion.

impl<T, E> FromStr for Constructible<T> where
    T: FromStr<Err = E>, 

Allows to parse directly into the cell.

type Err = E

The associated error which can be returned from parsing.

fn from_str(s: &str) -> Result<Self, Self::Err>

Parses a string s to return a value of this type.

impl<'a, T> IntoIterator for &'a Constructible<T>

Makes it possible to access the value with a for loop.

for value in &constructible {println! ("{}", value)}

type Item = &'a T

The type of the elements being iterated over.

type IntoIter = IntoIter<&'a T>

Which kind of iterator are we turning this into?

fn into_iter(self) -> Self::IntoIter

Creates an iterator from a value.