Access returns the result of loads through load proxy objects that implicity convert themselves to a template inferred type. This is a metaprogramming technique used to infer return types in C++.

However, I have heard requests that it would be great if it could be a bit smarter and do more than just be assigned to a type.

Example use cases that do not work today without workarounds:

  oop val = ...;
  narrowOop narrow = 0u;
  oop *oop_val = &val;
  narrowOop *narrow_val = &narrow;
  HeapWord *heap_word_val = reinterpret_cast<HeapWord*>(oop_val);

  if (val == HeapAccess<>::oop_load_at(val, 16)) {}
  if (HeapAccess<>::oop_load_at(val, 16) == val) {}
  if (val != HeapAccess<>::oop_load_at(val, 16)) {}
  if (HeapAccess<>::oop_load_at(val, 16) != val) {}

  if (HeapAccess<>::oop_load(oop_val) != val) {}
  if (HeapAccess<>::oop_load(heap_word_val) != val) {}
  if (RawAccess<>::oop_load(narrow_val) != narrow) {}

  if (HeapAccess<>::oop_load(oop_val) == val) {}
  if (HeapAccess<>::oop_load(heap_word_val) == val) {}
  if (RawAccess<>::oop_load(narrow_val) == narrow) {}

  if (val != HeapAccess<>::oop_load(oop_val)) {}
  if (val != HeapAccess<>::oop_load(heap_word_val)) {}
  if (narrow != RawAccess<>::oop_load(narrow_val)) {}

  if (val == HeapAccess<>::oop_load(oop_val)) {}
  if (val == HeapAccess<>::oop_load(heap_word_val)) {}
  if (narrow == RawAccess<>::oop_load(narrow_val)) {}

  if ((oop)HeapAccess<>::oop_load(oop_val) == NULL) {}

  oop tmp = true ? HeapAccess<>::oop_load(oop_val) : val;