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I'd say it would decrease predictability and readability. I'm not aware
of any language that treats "," as vararg concatenation. Some languages
have special "spread" operators. Lua simply declares that all returns of
last item of an explist are preserved to make multiple value returns usable.

Back to your example: If both f() and g() return varargs and the varargs
are concatenated, it'd make for very unreadable code. You'd always have
to know the arities of all function calls inside an explist ("h(f(),
g())", "{f(), g()}", "a, b, c = f(), g()"). With the current
implementation, you can always match one value on the LHS to one exp on
the RHS, except for superfluous values on the LHS, which Lua matches to
additional return values on the RHS. With your proposed change, this
wouldn't be possible anymore. Tools like luacheck couldn't help you if
you had too many or too few values on the LHS.

On 27.07.22 12:02, Rodrigo Azevedo wrote:

I'm wondering why we can't use multiple returns in expressions like

local a,b,c = f(),g()

Why not stack the result of the expressions on the right side and name
the ordered resulting values accordingly?


Suppose Lua 5.4 changes such that

local f = function() return 1,2 end
local g = function() return 3 end


local a,b,c,d = f(),g()

would simply do a=1,b=2,c=3,d=nil instead of the current

Moreover, the same on function arguments

s(f(),g()) -> calls s(1,2,3) instead of s(1,3).

Would it be more convenient and predictable?