Note this uses a slightly different access_type then the texture CL. We can either unify them and just limit storage to use read, read_write while texture uses read, write or we can have two productions.

Discussed at 2020-11-03 meeting.

I'll take one more crack at this. It goes back to the distinction between values (which are mathematical things) and variables (which are storage constructs in a computer).

From the spec, section Variable and const:

A variable is a named reference to storage that can contain a value of a particular storable type.

Two types are associated with a variable: its store type (the type of value that may be placed in the referenced storage) and its reference type (the type of the variable itself). If a variable has store type T and storage class S, then its reference type is pointer-to-T-in-S.

The store type is the thing we write after the colon. So in

    var foo :  i32;      

What we have is that foo is a named reference to (unique) storage, where that storage can hold an i32.

For a buffer variable, the store type describes the contents of the storage. We describe it with a struct with members (including layout. #1215).
The fact that you can write to those contents is a property of the thing that references the storage, not the values in the storage. We use the ordinary expressions in the language to do that reading and writing.

Contrast that with textures and samplers, which are opaque: they have no internal structure that we can poke at with WGSL expressions. There is no internal structure to the "store type".
We can only operate on textures and samplers via builtin functions. The only thing the type of a sampler or texture conveys is which builtin functions can operate on it. It's the builtins which determine whether they read or write.

So in sum:

• the struct type for a buffer is the store type: describes values. It doesn't capture the access kinds (readonly, readwrite)
• the texture or sampler has no internal structure to talk about, so everything, including access kinds is bound up into the type itself.

Discussed at 2020-11-17 meeting.

Updated to remove the access, read and read_write token. Uses the variable_declaration_list instead.