Suggestion: type(v, true) returns more detailed type

[Bruno Silvestre]

Hi,

Any chance of adding a boolean parameter to the type() function to return the more specific type? This would align with the "lua_is*()" functions from C and allow checking for more specific types in Lua code.

For example:
type(3) -- "number"
type(3, true) -- "integer"
type(3.14) -- "number"
type(3.14, true) -- "number"
type(lu) -- "userdata"
type(lu, true) -- "lightuserdata"
type(u) -- "userdata"
type(u, true) -- "userdata"
type(cf) -- "function"

type(cf, true) -- "cfunction"

regards

--

brunoos

[Sainan]

Could theoretically be implemented in pure Lua using math.type for int/float distinction, debug.getinfo to check for C functions, and pcall + setmetatable will give you the full type name of "light userdata".

-- Sainan

[Sainan]

function typex(v)
local t = type(v)
if t == "number" then
return math.type(v)
elseif t == "function" then
if debug.getinfo(v).short_src == "[C]" then
return "cfunction"
end
elseif t == "userdata" then
if string.find(select(2, pcall(setmetatable, v)), "got light userdata") then
return "lightuserdata"
end
end
return t
end

-- Sainan

[Tomás Guisasola]

Hi Bruno

> Any chance of adding a boolean parameter to the type() function to return the more specific type? This would align with the "lua_is*()" functions from C and allow checking for more specific types in Lua code.

Have you considered an alternative? type() could return two values:
the second one could be this more specific type.

Regards,
Tomás

[Dmitry Meyer]

On 2025-07-16 15:50, Tomás Guisasola wrote:

> Have you considered an alternative? type() could return two values:
> the second one could be this more specific type.

The change you've suggested is more invasive, some code may break if
type() suddenly starts to return two values instead of one.

[Spar]

typex is everything you need.

What would be better if type could be overridden by metamethods

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[Bas Groothedde]

> On 16 Jul 2025, at 18:06, Dmitry Meyer <m...@undef.im> wrote:

To be fair, there might be a lot of code that is written with the expectation that ‘type’ accepts one argument only. ‘type(func_with_2_results())’ might also break due to this change. Still, I think something like the OP suggestion would be useful.

~b

[eugeny gladkih]

imagine existing code

local a, b = type(some), 1

--
Yours sincerely, Eugeny.

[Sainan]

> local a, b = type(some), 1

Strange example because the return of type(some) will take up exactly 1 value, so b will always be 1.

Mulret only works on the last expression in a list.

-- Sainan

[Bruno Silvestre]

'typex' was my first option (in line with lua_tointegerx), but then I thought keeping 'type' would be more intuitive and avoid a new function.

The problem is the legacy code... I forget that people play around with Lua's parameter and return semantics a lot (the "A20 line" of Lua).

Well, I stick to the idea, even if the mechanism would be different.

regards

--

bruno

[Tomás Guisasola]

Hi

> > local a, b = type(some), 1
>
> Strange example because the return of type(some) will take up exactly 1 value, so b will always be 1.
>
> Mulret only works on the last expression in a list.

I doubt there are any declaration like:

local a, b = type(some)

But am not certain about:

local t = { type(some) }

Or:

f(type(some)) -- in the case that f accepts more than one value

Although I recognize this proposal (to let type return two values)
would introduce incompatibility, I don't think it would be a big
problem at all. Besides, I consider a boolean argument a very bad
choice, and also consider a second function (to work as almost the
same as the actual `type()`) as a waste. But this is a matter of
taste. Won't add much more to this discussion, though.

Regards,
Tomás

[Bruno Silvestre]

If the information can be quickly computed, it's a good idea... and using metamethods, one can return: type, subtype, subsubtype, etc.

I don't know if several subtypes are useful, but the flexibility is classy.

--

bruno

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[eugeny gladkih]

indeed, just drop “, 1” expecting b to be nil

--
Yours sincerely, Eugeny.