Macro starlark::starlark_simple_value

macro_rules! starlark_simple_value {
    ($x:ident) => { ... };
}

A macro reducing boilerplace defining Starlark values which are simple - they aren’t mutable and can’t contain references to other Starlark values.

Let’s define a simple object, where +x makes the string uppercase:

use allocative::Allocative;
use derive_more::Display;
use starlark::starlark_simple_value;
use starlark::values::Heap;
use starlark::values::NoSerialize;
use starlark::values::ProvidesStaticType;
use starlark::values::StarlarkValue;
use starlark::values::Value;
use starlark_derive::starlark_value;

#[derive(Debug, Display, ProvidesStaticType, NoSerialize, Allocative)]
struct MyObject(String);
starlark_simple_value!(MyObject);

#[starlark_value(type = "my_object")]
impl<'v> StarlarkValue<'v> for MyObject {
    // We can choose to implement whichever methods we want.
    // All other operations will result in runtime errors.
    fn plus(&self, heap: &'v Heap) -> starlark::Result<Value<'v>> {
        Ok(heap.alloc(MyObject(self.0.to_uppercase())))
    }
}

The starlark_simple_value! macro defines instances of ProvidesStaticType, AllocValue, AllocFrozenValue and UnpackValue. It also defines a method:

impl MyObject {
    pub fn from_value<'v>(x: Value<'v>) -> Option<&'v MyObject> {
        ...
    }
}