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".

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