function mod(&x) { x = 5; }  local x = 123; mod(x); print(x);

Result desired:

5

We know existing-Squirrel cannot do this, but is it possible to implement this in Squirrel sqvm.cpp and sqcompiler.cpp?

How to modify integers by reference, like C++ can do

void mod(int& x) { x = 5; } int x = 123; mod(x); printf("%i\n", x);

5

In Squirrel, the approximate thing is _OP_SETOUTER _OP_GETOUTER. It is used by closure functions

local x = 123; function mod() { x = 5; } mod(); print(x) // x is now 5

See _OP_SETOUTER _OP_GETOUTER MarkLocalAsOuter() GetOuterVariable() and FindOuter()

function mod()
-----OUTERS
0 x
-----Instructions
    [000]         _OP_LOADINT 5
    [001]        _OP_SETOUTER 255 0[x]  // could be extended to support true references
    [002]       _OP_LOADNULLS 1 1
    [003]          _OP_RETURN 255 0

local x = 123; function mod() { x = 5; } mod(); print(x)

5

With some modification, could real references be added to Squirrel / Squilu ?:

function mod(&x) { x = 5; }  local x = 123; mod(x); print(x);

5