• Subject: Re: Conditionally filling tables
• Date: Fri, 10 Mar 2006 11:57:08 +0200

```
I've used 'false' in such cases, as table hole fillers.

Condition1 and C or D,
Condition2 and E or false,

Simple, but not perfect..

Alexander Gladysh kirjoitti 10.3.2006 kello 8.59:

```
```Hi, all!

I need to create table (array), conditionally filled with elements.
Something like this (in pseudocode):

t =
{
A,
B,
if Condition1 then C else D end,
if Condition2 then E else nil end,
F
}

Problem is that second 'if' would generate gap in array if Condition2
is false. Of course I can iterate over array after its creation, and
close the gaps, which I would like to avoid.

Furthermore, (looks like) Lua syntax does not allow if statements to
appear inside table constructor, so I would have to use helper
function.

```
local iff = function(b, l, r) if b then return l else return r end end;
```t =
{
A,
B,
iff(Condition1, C, D),
iff(Condition2, E, nil),
F
}

I see another way with manually specifying indexes in array like this:

local index = 1
local nextindex = function()
local oldindex = index
index = index + 1
return oldindex
end

```
local iff = function(b, l, r) if b then return l else return r end end;
```local iffc = function(b, l, r)
if b then
if l then index = index + 1 end
return l
else
if r then index = index + 1 end
return r
end
end

t =
{
[nextindex()] = A,
[nextindex()] = B,
[nextindex()] = iff(Condition1, C, D),
[index] = iffc(Condition2, E, nil),
[nextindex()] = F
}

In this way, if branch with nil is selected, index is not incremented,
and nil array entry gets overridden with next element (F in the
example). (And if there is no next element, then it would be discarded
by Lua itself, so it is ok.)

While such approach looks suitable for my machine-generated case, I
would like to find some more user-friendly technique.

```