_ENV currently hates using classes. I'm attempting to create a Latin kind of Lua, and some things can't precisely be made with _ENV but it's a lot more efficient. setfenv was being uncooperative as well.
The subsequent code keeps returning the old attempt to call a nil value error. It specifies line 20, in which loadstring() is being checked, and line 23, where in the main chunk it is calling the __latin() function.
function __latin(code)
__predecessor = [===[
function typographia(value)
print(value);
end
chorda = {};
chorda.__index = chorda;
function chorda.sub(chorda, cChorda, fChorda)
return string.sub(chorda, cChorda, fChorda);
end
function chorda:sub(chorda, cChorda, fChorda)
return string.sub(chorda, cChorda, fChorda);
end
--[[ define values --]]
_ENV = {salve="Salve, munde!",typographia=typographia,print=print,chorda=chorda,chorda.sub=chorda.sub}; ]===];
__finalizer = __predecessor .. " " .. code;
local status, err = pcall(loadstring(__finalizer));
print(err);
if (err == nil) then loadstring(__finalizer)(); end
end
__latin('typographia(salve); chorda.sub(salve, 1, 3);');
You're getting "attempt to call a nil value" because loadstring returns nil (so you're calling pcall with nil). loadstring returns nil because the code you're compiling (__predecessor) contains invalid Lua:
_ENV = {
chorda.sub = chorda.sub -- can't do this
}
FYI: The loadstring/pcall stuff is irrelevant to your problem. Had you stripped it out before posting, you would have found this error yourself.
Related
hope you having great day , i'm test some stuff with lua, and i got some error
i have this codes in Object.lua
local Object = {name = "Object"}
Object.__index = Object
function Object.new()
local t = setmetatable({}, Object)
return t
end
function Object:keys(table)
local keyset={}
local n=0
for k,v in pairs(table) do
n=n+1
keyset[n]=k
end
return keyset
end
return Object
and i call Object.keys in "Other" script like this
local Object = require("lua.app.common.utils.Object")
local t = {
[1] = a,
[2] = b,
[3]= c
}
Object.keys(t)
and this cause error with
Exception has occurred: bad argument #1 to 'for iterator' (table expected, got nil),
because the parameter 'table' is passed as nil ( i don't know why thuogh debug mode just says its a nil)
on the other hand, if i fix object.keys(table) to object:keys(table), everything works fine, why this error happening?
Declaring the method keys with a colon adds an implicit self parameter as the first argument which requires you to call the method in the same way, using the colon.
Calling the method with the period notation expects you to supply the self parameter but because you only pass in t this is interpreted as self and then nil is added for your table parameter.
Declaring the method with a colon you actually have this
function Object:keys(self, table)
but calling it with the period means you have done this
Object.keys(t, nil)
hence the "table expected, got nil" error
What I want to avoid is to capture/ignore the exception when FFI calls a non-existent method.
For example, the following code calls the non_existent_method. However, pcall cannot handle the error.
local ffi = require "ffi"
local C = ffi.C
ffi.cdef [[
int non_existent_method(int num);
]]
local ok, ret = pcall(C.non_existent_method, 1)
if not ok then
return
end
I got the following error with OpenResty/lua-nginx-module.
lua entry thread aborted: runtime error: dlsym(RTLD_DEFAULT, awd): symbol not found
One more apporach would be to call the index metamethod directly:
You might want to wrap that into a function:
local ffi_mt = getmetatable(ffi.C)
function is_valid_ffi_call(sym)
return pcall(ffi_mt.__index, ffi.C, sym)
end
example:
ffi.cdef[[void (*foo)();]]
ffi.cdef[[int puts(const char *);]]
a,func = is_valid_ffi_call("foo")
-- false, "error message: symbol not found or missing declaration, whatever it is"
a,func = is_valid_ffi_call("puts")
-- true, cdata<int ()>: 0x7ff93ad307f0
One possible solution would be wrapping the C.non_existent_method call with a lua function.
For example
local ok, ret = pcall(function()
return C.non_existent_method(len)
end)
if not ok then
......
end
How do I invoke a class method using pcall in Lua?
I tried pcall(instance:method, arg) but it doesn't work.
I also tried pcall(instance.method, instance, arg) but that doesn't work either.
I googled for a solution but I couldn't get one.
An example:
local ValueOwnerMap = {}
ValueOwnerMap.__index = ValueOwnerMap
function ValueOwnerMap:create(key_prefix)
local instance = {}
setmetatable(instance, ValueOwnerMap)
instance.key = key_prefix .. ':value-owner-map'
return instance
end
function ValueOwnerMap:get(value)
return redis.call('HGET', self.key, value)
end
function ValueOwnerMap:put(value, owner_id)
return redis.call('HSETNX', self.key, value, owner_id)
end
function ValueOwnerMap:del(value)
return redis.call('HDEL', self.key, value)
end
local value_owner_map = ValueOwnerMap:create('owner:key')
local success, data = pcall(value_owner_map:put, 'a_value', 'a_owner_id')
instance:method(arg) is sugar for instance.method(instance,arg). So try
pcall(value_owner_map.put, value_owner_map, 'a_value', 'a_owner_id')
The following line replaces the last line of the block in the question. It works.
local success, data = pcall(function () value_owner_map:put('a_value', 'a_owner_id') end)
Thank you all for sharing
pcall (f, arg1, ยทยทยท)
Calls function f with the given arguments in protected mode. This means that any error inside f is not propagated; instead, pcall catches the error and returns a status code. lua ref
But Calls for functions in protected mode have some limitations especially when you are using ':' operator 'so-called synthetic sugar' of lua.
one way to WAR this limitation is to put inside a function
pcall(function () value_owner_map:put('a_value', 'a_owner_id') end)
This approach also catches the errors as usual:
local ok, msg = pcall(function () error('Phony Error') end)
if ok then
print("No error")
else
print("Got error".. tostring(msg))
end
-- Result:
-- Got error test.lua:53: Phony Error
I have a lua table which I used to share values between files. But I am getting confused in the following case
utility.lua file
M = {}
M.host_url = '192.168.0.1'
function M.myFunc()
print(M.host_url )
end
return M
in my main.lua
utility = require('utility')
utility.myFunc() -- this gives me 'a nil value' error
I get an error (nil value) for the host_url?
In M.myFunc doing only print action that function nothing will be return.in your utility file returning whole array see he below code that will clear your doudt.
In main.lua
utility = require('util')
value = utility.host_url
print(value)
In this example, I'm using lunit and am attempting to inject an instance method in to an instance of LuaSocket and am failing to see why the following isn't working.
-- Using lunit for unit testing
local lunit = require('lunitx')
_ENV = lunit.module('enhanced', 'seeall')
local socket = require('socket')
-- connect(2) to the service tcp/echo
local conn, connErr = socket.connect('127.0.0.1', '7')
function conn:receiveLine(...)
local line, err = self:receive('*l')
assert_string(line, err)
return line
end
function conn:sendLine(...)
local bytesSent, err = self:send(... .. '\n')
assert_number(bytesSent, err)
return bytesSent
end
The error message I'm getting is:
attempt to call method 'sendLine' (a nil value)
?? This seems like there is something obvious happening here, but I'm missing the required detail.
Ass-u-me'ing getmetatable(conn).__index == getmetatable(conn) source of confusion.
In this case, conn's metatable's __index metamethod is pointing to a different table than expected, so method resolution isn't happening against the table at getmetatable(conn).
function setup()
-- Update the table at __index, not conn's metatable
local mt = getmetatable(conn).__index
function mt:receiveLine(...)
local line, err = self:receive('*l')
assert_string(line, err)
return line
end
function mt:sendLine(...)
local bytesSent, err = self:send(... .. '\n')
assert_number(bytesSent, err)
return bytesSent
end
end
I was able to tease this out by testing to see if __index was pointing to conn's metatable, which it wasn't:
assert_equal(getmetatable(conn), getmetatable(conn).__index)
Generically, if there is a __newindex handler on getmetatable(conn) that is intercepting new table entries, use rawset() on __index's table.