Featurescript: passing by reference.

jrs_spedley · April 2019

I keep getting stung by passing by reference.

I have a multi dimension array which I am recursively parsing but the only way I can get it to work is if every item is in a box.

e.g as a trivial example ...

var x=new box([new box(1), new box(2), new box( [new box(3), new box(4)] ) ]);
output(x);
clear(x);
output(x);
    
function clear(x is box) {
    for (var y in x[]) {
        if (y[] is array)
            clear(y);
        else
            y[]=0;
    }
}

function output(x is box) {
    for (var y in x[]) {
        if (y[] is array)
            output(y);
        else
            print(y[]);
    }
}

I did try returning the array to the same variable in the hope that it would replace it but that doesn't work either ...

var x=[1, 2, [3, 4] ];
x=clear(x);
print(x);
    
function clear(x) {
    for (var y in x) {
        if (y is array)
            y=clear(y);
        else
            y=0;
    }
    return x;
}

Am I missing something or is the only way to do it like the first example?

konstantin_shiriazdanov · April 2019

arrays are "immutable" you should create a copy of array

function clear(x) {
var xCleared = [];
    for (var y in x) {
        if (y is array)
            xCleared = append(xCleared, clear(y));
        else
            xCleared = append(xCleared, 0);<br>    }
    return xCleared;<br>}

ilya_baran · April 2019

Konstantin's solution is also the right thing to do from a performance point of view (append is actually faster than modifying an array via x[i] = blah;)

jrs_spedley · April 2019

Ah, that explains a lot. My structure isn't changing, just the values so I can pass the arrays by value and put the values in boxes. Not perfect but I can manage with that. Thanks.

var x=[new box(1), new box(2),  [new box(3), new box(4)]  ];
clear(x);
output(x);
    
function clear(x is array) {
    for (var y in x) {
        if (y is array)
            clear(y);
        else
            y[]=0;
    }
}

function output(x is array) { for (var y in x) { if (y is array) output(y); else print(y[]); } }

konstantin_shiriazdanov · April 2019

I can't really understand why you had to wrap everything in boxes? are you trying to implement something like "set" datastructure?

jrs_spedley · April 2019

I have a many parts within parts and their positions and sizes are not determined until the whole structure has been processed, hence changing the data in a recursive fashion and the use of boxes to achieve this.
I use a first pass to calculate minimum sizes and number of parts in each subpart and then a second pass using the dimensions from the first pass to create the parts.

I would have used a different method if I'd have known passing by reference was such a problem when I started!

konstantin_shiriazdanov · April 2019

then you could also try to change array item by iterator:

function clear(x) {
    for (i=0; i < size(x); i+=1) {
        if (x[i] is array)
            x[i] = clear(x[i]);
        else
            x[i] = 0;<br>    }
    return x;<br>}

jrs_spedley · April 2019

Yes, I was trying iterating but kept crashing onShape (it would fail to update the part studio and logging out and back in would log me in twice).

I though it was a problem with featurescript as I couldn't see any errors but I'll try again, making a mistake is easy when you try and change code to function differently.

konstantin_shiriazdanov · April 2019

jrs_spedley said:
I use a first pass to calculate minimum sizes and number of parts in each subpart and then a second pass using the dimensions from the first pass to create the parts.

For case like that i would propose to make associated data structures - iterate through original array and add array items to the map structure with the fields which contain the item itself, and item "metadata". On the new passes you can add more associated data keeping it all in one place

Featurescript: passing by reference.

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