Struct Property

pub struct Property<T> { /* private fields */ }

Placeholder type for exported properties with no backing field.

This is the go-to type whenever you want to expose a getter/setter to GDScript, which does not directly map to a field in your struct. Instead of adding a useless field of the corresponding type (which needs initialization, extra space, etc.), you can use an instance of this type as a placeholder.

Property is a zero-sized type (ZST) which has exactly one value: Property::default(). It implements most of the basic traits, which allows its enclosing struct to remain composable and derive those traits itself.

When to use Property<T> instead of T

The following table shows which combinations of #[property] attributes and field types are allowed. In this context, get and set behave symmetrically, so only one of the combinations is listed. Furthermore, get_ref can be used in place of get, when it appears with a path.

Field type ➡ Attributes ⬇	bare T	Property<T>
#[property]	✔️ default get + set	❌️
#[property(get, set)] (same as above)	✔️ default get + set	❌️
#[property(get)]	✔️ default get (no set)	❌️
#[property(get="path")]	⚠️ custom get (no set)	✔️ custom get (no set)
#[property(get="path", set)]	✔️ custom get, default set	❌️
#[property(get="path", set="path")]	⚠️ custom get + set	✔️ custom get + set

“⚠️” means that this attribute combination is allowed for bare T, but you should consider using Property<T>.

Since there is no default get or set in these cases, godot-rust will never access the field directly. In other words, you are not really exporting that field, but linking its name and type (but not its value) to the specified get/set methods.

To decide when to use which:

• If you access your field as-is on the Rust side, use bare T.
  With a Property<T> field on the other hand, you would need to additionally add a T backing field.
• If you don’t need a backing field, use Property<T>.
  This is the case whenever you compute a result dynamically, or map values between Rust and GDScript representations.

Examples

Read/write accessible:

#[derive(NativeClass)]
struct MyObject {
    #[property]
    color: Color,
}

Read-only:

#[derive(NativeClass)]
struct MyObject {
    #[property(get)]
    hitpoints: f32,
}

Read-write, with validating setter:

#[derive(NativeClass)]
struct MyObject {
    #[property(get, set = "Self::set_name")]
    player_name: String,
}

#[methods]
impl MyObject {
    fn set_name(&mut self, _owner: TRef<Reference>, name: String) {
        if validate(&name) {
            self.player_name = name;
        }
    }
}

Write-only, no backing field, custom setter:

#[derive(NativeClass)]
struct MyObject {
    #[property(set = "Self::set_password")]
    password: Property<String>,
}

#[methods]
impl MyObject {
    fn set_password(&mut self, _owner: TRef<Reference>, password: String) {
        // securely hash and store password
    }
}

Trait Implementations

impl<T: Clone> Clone for Property<T>

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

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl<T: Debug> Debug for Property<T>

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

Formats the value using the given formatter.

impl<T: Default> Default for Property<T>

fn default() -> Property<T>

Returns the “default value” for a type.

impl<T: Hash> Hash for Property<T>

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

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> Ord for Property<T>

fn cmp(&self, other: &Property<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> PartialEq for Property<T>

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

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

const 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> PartialOrd for Property<T>

fn partial_cmp(&self, other: &Property<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: Copy> Copy for Property<T>

impl<T: Eq> Eq for Property<T>

impl<T> StructuralPartialEq for Property<T>