Trait Data

Source

pub trait Data: Clone + 'static {
    // Required method
    fn same(&self, other: &Self) -> bool;
}

Expand description

A trait used to represent value types.

These should be cheap to compare and cheap to clone.

See https://sinusoid.es/lager/model.html#id2 for a well-written explanation of value types (albeit within a C++ context).

§Derive macro

In general, you can use derive to generate a Data impl for your types.

#[derive(Clone, Data)]
enum Foo {
    Case1(i32, f32),
    Case2 { a: String, b: Arc<i32> }
}

§Derive macro attributes

There are a number of field attributes available for use with derive(Data).

#[data(ignore)]

Skip this field when computing sameness.

If the type you are implementing Data on contains some fields that are not relevant to the Data impl, you can ignore them with this attribute.

#[data(same_fn = "path")]

Use a specific function to compute sameness.

By default, derived implementations of Data just call Data::same recursively on each field. With this attribute, you can specify a custom function that will be used instead.

This function must have a signature in the form, fn<T>(&T, &T) -> bool, where T is the type of the field.

§Collection types

Data is not implemented for std collection types, because comparing them can be expensive. To use collection types with Druid, there are two easy options: either wrap the collection in an Arc, or build druid with the im feature, which adds Data implementations to the collections from the im crate, a set of immutable data structures that fit nicely with Druid.

If the im feature is used, the im crate is reexported from the root of the druid crate.

§Example:

#[derive(Clone, Data)]
struct PathEntry {
    // There's no Data impl for PathBuf, but no problem
    #[data(eq)]
    path: PathBuf,
    priority: usize,
    // This field is not part of our data model.
    #[data(ignore)]
    last_read: Instant,
}

§C-style enums

In the case of a “c-style” enum (one that only contains unit variants, that is where no variant has fields), the implementation that is generated checks for equality. Therefore, such types must also implement PartialEq.

Required Methods§

Source

fn same(&self, other: &Self) -> bool

Determine whether two values are the same.

This is intended to always be a fast operation. If it returns true, the two values must be equal, but two equal values need not be considered the same here, as will often be the case when two copies are separately allocated.

Note that “equal” above has a slightly different meaning than PartialEq, for example two floating point NaN values should be considered equal when they have the same bit representation.

Dyn Compatibility§

This trait is not dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety", so this trait is not object safe.

Trait DataCopy item path

§Derive macro

§Derive macro attributes

§Collection types

§Example:

§C-style enums

Required Methods§

fn same(&self, other: &Self) -> bool

Dyn Compatibility§

Implementations on Foreign Types§

impl Data for &'static str

fn same(&self, other: &Self) -> bool

impl Data for IpAddr

fn same(&self, other: &Self) -> bool

impl Data for SocketAddr

fn same(&self, other: &Self) -> bool

impl Data for ErrorKind

fn same(&self, other: &Self) -> bool

impl Data for bool

fn same(&self, other: &Self) -> bool

impl Data for char

fn same(&self, other: &Self) -> bool

impl Data for f32

fn same(&self, other: &Self) -> bool

impl Data for f64

fn same(&self, other: &Self) -> bool

impl Data for i8

fn same(&self, other: &Self) -> bool

impl Data for i16

fn same(&self, other: &Self) -> bool

impl Data for i32

fn same(&self, other: &Self) -> bool

impl Data for i64

fn same(&self, other: &Self) -> bool

impl Data for i128

fn same(&self, other: &Self) -> bool

impl Data for isize

fn same(&self, other: &Self) -> bool

impl Data for u8

fn same(&self, other: &Self) -> bool

impl Data for u16

fn same(&self, other: &Self) -> bool

impl Data for u32

fn same(&self, other: &Self) -> bool

impl Data for u64

fn same(&self, other: &Self) -> bool

impl Data for u128

fn same(&self, other: &Self) -> bool

impl Data for ()

fn same(&self, _other: &Self) -> bool

impl Data for usize

fn same(&self, other: &Self) -> bool

impl Data for String

fn same(&self, other: &Self) -> bool

impl Data for Ipv4Addr

fn same(&self, other: &Self) -> bool

impl Data for Ipv6Addr

fn same(&self, other: &Self) -> bool

impl Data for SocketAddrV4

fn same(&self, other: &Self) -> bool

impl Data for SocketAddrV6

fn same(&self, other: &Self) -> bool

impl Data for RangeFull

fn same(&self, other: &Self) -> bool

impl Data for Duration

fn same(&self, other: &Self) -> bool

impl Data for Instant

fn same(&self, other: &Self) -> bool

impl Data for SystemTime

fn same(&self, other: &Self) -> bool

impl Data for NonZeroI8

fn same(&self, other: &Self) -> bool

impl Data for NonZeroI16

fn same(&self, other: &Self) -> bool

impl Data for NonZeroI32

fn same(&self, other: &Self) -> bool

impl Data for NonZeroI64

fn same(&self, other: &Self) -> bool

impl Data for NonZeroI128

fn same(&self, other: &Self) -> bool

Trait Data