How does order factor in, if the code refers to them by name? I think
I'm overlooking something.
In Rio Lua, the order is as they appear. So if a global access
appears before any other upvalue access on a function, _ENV is the
first upvalue.
local u2, u3, u4, u5
function()
print(u2, u3, u4, u5) -- _ENV is the first upvalue, because
"print" is actually "_ENV.print" (or "_ENV['print']")
end
Unless I'm missing something, I don't think this is reliable, that's
an implementation detail, and could change any future version, even a
patch release of 5.3.
The Lua 5.3 manual states: "Upvalues have no particular order, as they
are active through the whole function. They are numbered in an
arbitrary order."
I'd probably recommend finding a different way to achieve this for a
public module.
- Claire