handling arguments in Lua function with variable number of arguments

Question

I was trying to write a function with a variable number of arguments which do something for all its number entries. so I came up with something like this:

function luaFunc (...)
   for i,v in ipairs{...} do
      if type(v)=='number' then
         --do something
      end
   end
end

but when i run this, it stops right on first non-number argument. whats the problem?

It stops at the first nil argument not at the first non-number argument. — lhf
– lhf, Commented Mar 25, 2013 at 12:25
if you read the docs for ipairs, it specifically tells you that it does this. i think what you are looking for here is the pairs function, which iterates all keys in a table (not necessarily in order). — Mike Corcoran
– Mike Corcoran, Commented Mar 25, 2013 at 16:26

Egor Skriptunoff · Accepted Answer · 2013-03-25 12:31:34Z

1

local function luaFunc (...)
   for i = 1, select('#',...) do
      local v = select(i,...)
      if type(v)=='number' then
         --do something
         print(v)
      end
   end
end
luaFunc (1,'a',nil,2)     ]

-- Output
1
2

answered Mar 25, 2013 at 12:31

Egor Skriptunoff

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Comments

lhf · Accepted Answer · 2013-03-25 14:20:21Z

1

Try also this:

function luaFunc (...)
   local t=table.pack(...)
   for i=1,t.n do
      local v=t[i]
      if type(v)=='number' then
         print(i,v)
      end
   end
end

luaFunc(10,20,"hello",40,nil,60,print,99)

answered Mar 25, 2013 at 14:20

lhf

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4 Comments

VahidM Over a year ago

also useful. thank you. btw why should the iteration with ipairs not work? the element has a key and has a value which is nil ..

lhf Over a year ago

@VahidM, ipairs uses the # operator on the table to determine how many elements it has but # is not useful for tables with holes (nil entries).

VahidM Over a year ago

I've just tested # operator for a table with nil entries and it worked fine. It must be something else. thank you anyway.

lhf Over a year ago

@VahidM, try N=100; t={}; for i=1,N do t[i]=i end; t[64]=nil; print(#t).

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