Re: Arithmetic on table fields passed as function argument
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- Subject: Re: Arithmetic on table fields passed as function argument
- From: Andrew Starks <andrew.starks@...>
- Date: 2013年9月14日 20:41:39 -0500
On Saturday, September 14, 2013, Jayanth Acharya wrote:
Admittedly, I have adopted a lazy and somewhat (perhaps) unconventional approach to learning Lua, i.e. by trying out what I've learnt so far supplanted by a bit of intuition.
Here's one snippet that stumped me. Lua didn't like me doing arithmetic on table fields, but from what I've read so far, I couldn't figure out an obvious reason.
t = {}
t.distance = 40
t.time = 2.5
for k,v in pairs(t) do print(k,v) end
function speed(tab) return tab.distance/tab.time end
t.speed = speed{t}
for k,v in pairs(t) do print(k,v) end
[/code]
Lua barfs out this output:-
[output]time 2.5
distance 40
lua: 8.lua:7: attempt to perform arithmetic on field 'distance' (a nil value)
stack traceback:
8.lua:7: in function 'speed'
8.lua:9: in main chunk
[C]: ?
[/output] Why so ?
Your call to speed is the problem:
speed{t}
Wraps t in a table so that:
Speed gets tab[1].distance has what you want.
Change the call to speed(t)
The {} variant is used when you want to make named arguments.
speed{distance= 40, time=2.5}
Would also work.
Now I'll try not to send this email 3 times.
-Andrew