@pmuetschard I'm still unsure why the original code was failing to update the render pass object, any thoughts?

@mikes-lunarg, how did you manage to notice the discrepancy -- examining the state in AGI perhaps?

@mark-lunarg That's exactly how I found it. As an extra sanity check I went looking for the new extension data in the state tab of AGI and it wasn't there.

Map access operations return a value not a reference.
See https://github.com/google/agi/tree/master/gapil#map (although that could probably be a bit clearer)
So given that:

renderPass.AttachmentDescriptions[j] returns a value
renderPass.AttachmentDescriptions[j].StencilLayout gives you a temporary, then sets the value on that temporary, then discards it.

Map access operations return a value not a reference. See https://github.com/google/agi/tree/master/gapil#map (although that could probably be a bit clearer) So given that:

renderPass.AttachmentDescriptions[j] returns a value renderPass.AttachmentDescriptions[j].StencilLayout gives you a temporary, then sets the value on that temporary, then discards it.

Makes sense, thanks for the info!

Map access operations return a value not a reference. See https://github.com/google/agi/tree/master/gapil#map (although that could probably be a bit clearer) So given that:

renderPass.AttachmentDescriptions[j] returns a value renderPass.AttachmentDescriptions[j].StencilLayout gives you a temporary, then sets the value on that temporary, then discards it.

Are the a difference in handling lvalue and rvalue?

Based on the change are these two examples are semantically different? @AWoloszyn

renderPass.AttachmentDescriptions[j] = AttachmentDescripton(...)

attachmentDescription := AttachmentDescripton(...)
renderPass.AttachmentDescriptions[j] = attachmentDescripton

Based on the change are these two examples are semantically different? @AWoloszyn

renderPass.AttachmentDescriptions[j] = AttachmentDescripton(...)

attachmentDescription := AttachmentDescripton(...)
renderPass.AttachmentDescriptions[j] = attachmentDescripton

Those are the same. What would be different is

a := A(...)
a.foo = Foo()
blah.a[j] = a

a := A(...)
blah.a[j] = a
blah.a[j].foo = Foo()

The difference is that

blah.a[j].foo = Foo()

is a no-op.

This is something very subtle and error prone are there any way to fix this?

Map access operations return a value not a reference. See https://github.com/google/agi/tree/master/gapil#map (although that could probably be a bit clearer) So given that:
renderPass.AttachmentDescriptions[j] returns a value renderPass.AttachmentDescriptions[j].StencilLayout gives you a temporary, then sets the value on that temporary, then discards it.

Are the a difference in handling lvalue and rvalue?

This is more about with what value map[] returns. In psuedo-C it would look something like:

template<typename K, typename V>
class map {
    V operator[](K key);
};

This differs from a STD unordered_map which looks like

template<typename K, typename V>
class map {
    V& operator[](K key);
};

I.e. the [] operator in GAPIL returns a COPY of the element in the map, not a REFERENCE to the element in the map.

@yalcinmelihyasin What is our next step? Can we merge this fix or would you like to see additional changes?