Lua 5.4: question about label visibility rule
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- Subject: Lua 5.4: question about label visibility rule
- From: Arnaud Delobelle <arnodel@...>
- Date: 2022年1月19日 10:25:12 +0000
Hi all,
In the Lua 5.4 docs it says the following.
A label should not be declared where a label with the same
name is visible, even if this other label has been declared
in an enclosing block.
I have found the following test in the Lua 5.4.3 Test Suite (available
here: http://www.lua.org/tests/), in the file goto.lua (starting line
223):
local function testG (a)
if a == 1 then
goto l1
error("should never be here!")
elseif a == 2 then goto l2
elseif a == 3 then goto l3
elseif a == 4 then
goto l1 -- go to inside the block
error("should never be here!")
::l1:: a = a + 1 -- FIRST DECLARATION OF l1
else
goto l4
::l4a:: a = a * 2; goto l4b
error("should never be here!")
::l4:: goto l4a
error("should never be here!")
::l4b::
end
do return a end
::l2:: do return "2" end
::l3:: do return "3" end
::l1:: return "1" -- SECOND DECLARATION OF l1
end
In this function the label ::l1:: is declared twice, once in the
"elseif a == 4" clause and once at the end of the function. In my
understanding, the second declaration of this label is visible at the
point where the first declaration is made. That would contravene the
rule I have quoted above.
This must mean that I am misunderstanding the meaning of the quoted
rule. Could anyone please help me understand it?
Regards,
--
Arnaud