• Re: input/output parameters

    From Postiljon Petskin@21:1/5 to Anton Shepelev on Sat Apr 22 08:47:07 2023
    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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