On 07/27/2014 04:19 PM, Andrew Wagner wrote:
Is it possible to disallow re-binding of variables in lua?
This prevents global reassignments, which I think handles most pollution
issues:
do
local globals = {}
setmetatable(_G, {
__index = globals,
__newindex = function(table, key, value)
if globals[key] ~= nil then error('Redefining ' ..
tostring(key)) end
globals[key] = value
end
})
end
As a test:
a = 4
--a = 5 -- Error
print(a)
do
local x = 13
x = x - 10
local y = 27
z = x + y
end
print(z)
I used that at my previous job since we had a bunch of subprojects and
there was some pollution causing issues.
One thing that is clear is that in almost build specifications
(including all of mine), people are frequently mutating lists of
strings that get passed into compilers, and lists of dependencies. So
if you remove the ability to do stuff like:
FOO=-IA
(specify rule 1 using A)
FOO+=-IB
(specify rule 2 using B)
FOO+=-IC
(specify rule 3 using A and C, and also has B as cruft because the
programmer was lazy)
You need to have a very lightweight alternative. Maybe something like:
FOO=-IA
specify rule 1 needing A
(
FOO+=-IB
(specify rule 2 using B)
)
(
FOO+=-IC
(Specify rule 3 using A and C, with no B cruft since the programmer
wasn't allowed to be lazy)
)
You can use explicit blocks and locals to do that:
FOO='-lA'
do
local FOO = FOO..' -lB'
end
do
local FOO = FOO..' -lC'
end
print(FOO)
Cheers,
Rendaw
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