On Saturday, March 13, 2021 at 2:32:40 PM UTC+2, Anton Shepelev wrote:

Hello, all

I started learning JavaScript but yesterday, but am already
stuck at implementing input/output parameters. As I
understand, they are not part of the language, yet I find
them very convenient for normal procedural programming. For
example, they allow returning a boolean flag and using
functions inside `if` tests, similar to the very convenient
TryParse() and TryGetValue() functions in C#:

TryParse: https://docs.microsoft.com/en-us/dotnet/api/system.int32.tryparse TryGetValue: https://docs.microsoft.com/en-us/dotnet/api/system.collections.generic.dictionary-2.trygetvalue

Unfortunately for me, JavaScript seems to compensate the
lack of in/out parameters with much more complicated
functional and object-oriented mechanisms. I therefore have
tried to implement them myself, but have not come up with a
satisfactory solution. The examples below demonstrate a
function for integer division that stores the result in
variable and returns a boolean value indicating whether the
division was exact:

// for bi-direction in/out parameters, return a code that
// creates an anonymous object storing the the value *and*
// setter clousure:

function out_1(vn)
{ return "x => " + vn + " = x"; }

function int_div_1(a, b ,c)
{ var /*integer */ r; // ratio
var /*boolean */ x; // result is exact

r = Math.floor(a / b);
x = r * b === a;
c( r );
return x;
}

function out_2( vn, val, ret )
{ return `${vn} = ${val}, ${ret}`; }

function int_div_2(a, b, vn)
{ var /*integer */ r; // ratio
var /*boolean */ x; // result is exact

r = Math.floor(a / b);
x = r * b === a;
return out_2(vn, r, x);
}

{ let /*integer */ ratio;
let /*boolean */ exact;

exact = int_div_1(7, 3, eval(out_1("ratio")));
console.log(`7/3: ratio = ${ratio}; exact = ${exact}.`);

exact = int_div_1(6, 3, eval(out_1("r")));
console.log(`6/3: ratio = ${ratio}; exact = ${exact}.`);

exact = eval(int_div_2(7, 3, "ratio"));
console.log(`7/3: ratio = ${ratio}; exact = ${exact}.`);

exact = eval(int_div_2(6, 3, "ratio"));
console.log(`6/3: ratio = ${ratio}; exact = ${exact}.`);
}

Can you think of better way to emulate output parameters,
and preferable also bi-directional input/output parameters?

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