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Compile Lua without automatic conversion between strings and numbers

Lua is generally a strongly-typed language, providing almost no implicit conversion between data types.

However, numbers and strings do get automatically coerced in a few cases:

Lua provides automatic conversion between string and number values at run time. Any arithmetic operation applied to a string tries to convert this string to a number, following the rules of the Lua lexer. (The string may have leading and trailing spaces and a sign.) Conversely, whenever a number is used where a string is expected, the number is converted to a string, in a reasonable format

Thus:

local x,y,z = "3","8","11"
print(x+y,z)  --> 11   11
print(x+y==z) --> false
print(x>z)    --> true

I do not want this. How can I recompile the Lua interpreter to remove all automatic conversion?

I would prefer to have:

print(x+y)    --> error: attempt to perform arithmetic on a string value
print(x>1)    --> error: attempt to compare number with string
print(x..1)   --> error: attempt to concatenate a number value
like image 367
Phrogz Avatar asked Mar 05 '14 23:03

Phrogz


1 Answers

The illustrious LHF has commented above that this is not possible out of the box, and requires editing the innards of Lua, starting with http://www.lua.org/source/5.2/lvm.c.html#luaV_tonumber

Marking this as the answer in order to close this question. If anyone later chooses to provide an answer with in-depth details on what needs to be done, I will gladly switch the acceptance mark to that answer.

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Phrogz Avatar answered Oct 22 '22 15:10

Phrogz