Struct MutateValue 

pub struct MutateValue<'a, T = Any> { /* private fields */ }

A callback value carrying the engine’s in-place permission.

Unlike an owning typed argument, this handle does not increment the reference count. Borrow through it to inspect the node, then consume it in default_maybe_inplace_mutate to continue recursion. A surviving owning alias still forces copying. Node borrows come from this handle, not from the callback context, so the handle can safely be passed to another context. T selects the callback’s matched FFI type; Any matches every value.

A node borrow cannot survive consumption of the handle:

use tvm_ffi::{MutateContext, MutateValue};
fn invalid(value: MutateValue<'_>, ctx: &mut MutateContext<'_>) {
    let node = value.as_node::<tvm_ffi::collections::array::ArrayObj>().unwrap();
    ctx.default_maybe_inplace_mutate(value).unwrap();
    println!("{}", node.size);
}

Moving the handle into a nested callback cannot bypass that borrow:

use std::cell::RefCell;
use tvm_ffi::{structural_mutate, MutateContext, MutateValue};
fn invalid(value: MutateValue<'_>) {
    let node = value.as_node::<tvm_ffi::collections::array::ArrayObj>().unwrap();
    let pending = RefCell::new(Some(value));
    structural_mutate(true, |_: bool, inner: &mut MutateContext<'_>| {
        inner.default_maybe_inplace_mutate(pending.borrow_mut().take().unwrap())
    }).unwrap();
    println!("{}", node.size);
}

Implementations

impl<'a> MutateValue<'a>

pub fn borrowed(value: &'a StructuralView) -> Self

Wrap a borrowed value without granting in-place permission.

impl<'a, T> MutateValue<'a, T>

pub fn inplace_mode(&self) -> InplaceMode

Permission established before callback arguments acquire ownership.

pub fn as_value(&self) -> &StructuralView

Borrow the current value. The borrow must end before default mutation.

pub fn try_cast<U: ContainerElement>(self) -> Result<MutateValue<'a, U>, Self>

Narrow the matched type without acquiring an owning reference.

pub fn into_untyped(self) -> MutateValue<'a>

Erase the matched type while preserving the engine-issued permission.

Methods from Deref<Target = StructuralView>

pub fn to_owned(&self) -> Any

Copy this borrowed value into an owning Any.

pub fn cast<R: AnyCompatible>(&self) -> Option<R>

Convert the value into an owned typed handle.

pub fn type_index(&self) -> i32

Runtime type index stored in this value.

pub fn as_node<N: ObjectCore>(&self) -> Option<&N>

Borrow the value as node type N if it is an instance of that type.

Trait Implementations

impl<T> Deref for MutateValue<'_, T>

type Target = StructuralView

The resulting type after dereferencing.

fn deref(&self) -> &Self::Target

Dereferences the value.