Trait TraitView 

pub trait TraitView: Sized {
    const TAG: mx_tag;

    // Required method
    unsafe fn from_raw_parts(
        data: *mut c_void,
        vtable: *const c_void,
        owner: Option<SEXP>,
    ) -> Self;

    // Provided methods
    unsafe fn try_from_sexp(sexp: SEXP) -> Option<Self> { ... }
    unsafe fn try_from_sexp_or_error(
        sexp: SEXP,
        trait_name: &str,
    ) -> Result<Self, String> { ... }
}

Trait for view types that can be created from SEXP via trait dispatch.

This trait is implemented by the macro-generated <Trait>View structs. It provides a common interface for:

• Querying whether an object implements a trait
• Creating a view from an SEXP

Generated by #[miniextendr] on traits

When you write:

#[miniextendr]
pub trait Counter {
    fn value(&self) -> i32;
    fn increment(&mut self);
}

The generated view keeps its pointers in TraitViewData. Views made from an R external pointer root that owner until they are dropped; raw Rust-owned views instead require the caller to keep their data alive.

Usage

// Try to get a Counter view from an R object
let view = CounterView::try_from_sexp(obj)?;

// Call methods through the view
view.increment();
let val = view.value();

Safety

The from_raw_parts method is unsafe because:

• data must be a valid pointer to the RefCell holding the concrete object (the vtable’s shims borrow it for each call)
• vtable must be a valid pointer to the trait’s vtable
• The vtable must remain valid for the lifetime of the view
• The owner, when supplied, must keep data alive; otherwise the caller must keep data alive for the lifetime of the view

Required Associated Constants

const TAG: mx_tag

The type tag for this trait.

This is a compile-time constant generated by #[miniextendr] on the trait.

Required Methods

unsafe fn from_raw_parts( data: *mut c_void, vtable: *const c_void, owner: Option<SEXP>, ) -> Self

Create a view from raw data and vtable pointers.

Safety

• data must be a valid, non-null pointer to the RefCell holding the concrete object
• vtable must be a valid, non-null pointer to the trait’s vtable
• vtable must remain valid for the lifetime of the view
• owner, when present, must be a live R object owning data; the implementation must root it for the lifetime of the view
• Without an owner, the caller must keep data alive for that lifetime
• A call that conflicts with one still running on the same object raises the miniextendr_borrow_conflict error (the shims borrow its RefCell)
• Construction, use and drop must all run on R’s main thread

Provided Methods

unsafe fn try_from_sexp(sexp: SEXP) -> Option<Self>

Try to create a view from an R SEXP.

Queries the object for this trait’s vtable using mx_query. If the object implements the trait, returns Some(view). Otherwise returns None.

Safety

• sexp must be a valid R external pointer (EXTPTRSXP)
• The object must stay live through construction; the view then roots it
• A call that conflicts with one still running on the same object raises the miniextendr_borrow_conflict error (the shims borrow its RefCell)
• Construction, use and drop must all run on R’s main thread

Returns

• Some(Self) if the object implements the trait
• None if the object does not implement the trait

Example

let counter = unsafe { CounterView::try_from_sexp(obj) }
    .expect("Object does not implement Counter");

unsafe fn try_from_sexp_or_error( sexp: SEXP, trait_name: &str, ) -> Result<Self, String>

Try to create a view, returning an error message on failure.

Similar to try_from_sexp but returns an error string suitable for use as an R error message if the object does not implement the trait.

Safety

Same as try_from_sexp.

Dyn Compatibility

This trait is not dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety".

Implementors

impl TraitView for RCloneView

const TAG: mx_tag = TAG_RClone

impl TraitView for RCopyView

const TAG: mx_tag = TAG_RCopy

impl TraitView for RDebugView

const TAG: mx_tag = TAG_RDebug

impl TraitView for RDefaultView

const TAG: mx_tag = TAG_RDefault

impl TraitView for RDisplayView

const TAG: mx_tag = TAG_RDisplay

impl TraitView for RErrorView

const TAG: mx_tag = TAG_RError

impl TraitView for RFromStrView

const TAG: mx_tag = TAG_RFromStr

impl TraitView for RHashView

const TAG: mx_tag = TAG_RHash

impl TraitView for RIteratorView

const TAG: mx_tag = TAG_RIterator

impl TraitView for ROrdView

const TAG: mx_tag = TAG_ROrd

impl TraitView for RPartialOrdView

const TAG: mx_tag = TAG_RPartialOrd