Sketching dvm object.

dvm-lib/src/vm/mod.rs

@@ -10,6 +10,7 @@ use std::rc::Rc;
 
 pub mod constant;
 pub mod function;
+pub mod object;
 pub mod value;
 
 pub struct DvmContext {

dvm-lib/src/vm/object.rs

@@ -0,0 +1,50 @@
+use crate::vm::value::Value;
+use std::alloc::{Layout, alloc};
+
+#[repr(C)]
+pub struct Object {
+    header: ObjectHeader,
+    fields: [Value],
+}
+
+pub struct ObjectHeader {
+    field_count: usize,
+}
+
+fn get_object(field_count: usize) -> Box<Object> {
+    let (layout, fields_base) = Layout::array::<Value>(field_count)
+        .and_then(|fields_array_layout| Layout::new::<ObjectHeader>().extend(fields_array_layout))
+        .unwrap();
+    println!("{:?}", layout);
+    let ptr = unsafe { alloc(layout) };
+    if ptr.is_null() {
+        panic!("failed to allocate memory");
+    }
+    unsafe {
+        ptr.cast::<ObjectHeader>()
+            .write(ObjectHeader { field_count });
+        let fields_ptr = ptr.add(fields_base).cast::<Value>();
+        // initialize each field to Value::Null
+        for i in 0..field_count {
+            fields_ptr.add(i).write(Value::Null);
+        }
+
+        // this is somehow magic
+        // https://stackoverflow.com/questions/64120001/how-to-create-a-smart-pointer-to-an-unsized-type-with-an-embedded-slice
+        Box::from_raw(std::ptr::slice_from_raw_parts(ptr as *mut Value, field_count) as *mut Object)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn melt_the_processor() {
+        let mut o = get_object(3);
+        assert_eq!(o.header.field_count, 3);
+        assert_eq!(o.fields.len(), 3);
+        o.fields.fill(Value::Int(42));
+        assert!(o.fields.iter().all(|v| *v == Value::Int(42)));
+    }
+}