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) -> 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 macro generates CounterView that implements TraitView:

impl TraitView for CounterView {
    const TAG: mx_tag = TAG_COUNTER;

    unsafe fn from_raw_parts(data: *mut c_void, vtable: *const c_void) -> Self {
        Self {
            data,
            vtable: vtable.cast::<CounterVTable>(),
        }
    }
}

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 concrete object
• vtable must be a valid pointer to the trait’s vtable
• The pointers must remain valid 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) -> Self

Create a view from raw data and vtable pointers.

Safety

• data must be a valid, non-null pointer to the concrete object
• vtable must be a valid, non-null pointer to the trait’s vtable
• Both pointers must remain valid for the lifetime of the view

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)
• Must be called 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", so this trait is not object safe.

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