Function variables

james_sleeman

It would be super useful to be able to define a variable as a function, so that we could do something like

#myFunctionVariable(5)

where

#myFunctionVariable(x) = [equation involving x]

use case for example would be in having some standard and centrally configurable adjustment for hole sizes, to achieve dimensionally accurate holes on 3d printers without having to hard-code in your printer/filament's peculiarities we could just dimension our 3mm holes to #hole(3) such that the #hole(x) variable was defined as an equation that produces the correctly adjusted dimension. 

ilya_baran

With FeatureScript released, you can now do basically this, just using a Feature Studio.  Create a custom feature with code like this:

annotation { "Feature Type Name" : "Add My Functions" }
export const addMyFunctions = defineFeature(function(context is Context, id is Id, definition is map)
    precondition
    {
    }
    {
        setVariable(context, "myFunctionVariable",
            function(x) {
                return x + 2 * millimeter; // Function code goes here
            }
        );
        // You can make more setVariable calls here to make more functions
    });

And then in your Part Studio, add the "Add My Functions" feature at the beginning of the feature list.  You can then use #myFunctionVariable(2 cm) in a subsequent expression (to get 22mm).  Eventually we'll make it possible to just set the value by defining the myFunctionVariable variable without creating a Feature Studio.

pablo_fernandez_tech

I tried this, but I get "Enter a valid expression" when I try to use the function:

ilya_baran

It's impossible to debug without a link to a public document.  A possible explanation is that your function is not returning a quantity with the right units -- it needs to return a length.

chadstoltzfus

I was very curious to try this out and it turns out that there's a lot you can do with these functions, at least a lot more than I thought. They're a pain to debug and you miss out on the great snippet inserts you get in Feature Studios, but it's cool that things like for loops work in variables.

Here's a variable that displays a decimal as a fraction (just paste this into the Value field of a variable feature).

function(x){var wholeNumber = floor((x + 1e-11 * meter) / inch);var remainder = x / inch - wholeNumber;var fraction = 1;for (var i = 0; i < 8; i += 1){if (abs(remainder - round(remainder)) < 1e-11) { break;}remainder *= 2;fraction *= 2;}if (fraction == 1){return wholeNumber ~ "\"";     }  var fractionalPart = round(remainder) ~ "/" ~ fraction;if (wholeNumber == 0){return fractionalPart ~ "\"";}return wholeNumber ~ " " ~ fractionalPart ~ "\""; }




This is definitely one of those "why would you ever do this" sort of situations, as it is way more efficient and simpler to just write a custom feature, but who knows there might be some cases where it's better to just use a variable. One could imagine a variable studio of functions that one might want to use often. 

Evan_Reese

chadstoltzfus said:

One could imagine a variable studio of functions that one might want to use often. 

This is definitely fascinating, but I agree that I can't quite picture the use-case where that's better than a feature. There probably is one somewhere though.

Evan_Reese

pablo_fernandez_tech said:

I tried this, but I get "Enter a valid expression" when I try to use the function:

If you're using Ilya's code above you need to add units to the number since you can't add a number, and length together. Try #myFunctionVariable(2mm) instead.

pablo_fernandez_tech

The problem was that I didn't have a unit.

fst

I cannot get this to work. Have defined a function as value of a parameter as shown by @chadstoltzfus. Now I try to call it, but it is always shown as invalid.

Function definition: pipe_width_at: function(x){return pipe_height_at_bottom-(pipe_width_at_bottom-pipe_width_at_top)*pos/soundpipe_length;}

^^This still seems to work! (All variables inside this definition are defined above, they are lengths in mm. Couldn't define the function as length, it was accepted when I chose "any" though.)

Attempts to instantiate the function:
#pipe_width_at(#soundpipe_length+#soundhole_length)

#pipe_width_at(245mm)

#pipe_width_at(245)

^^ None of these seem to work.
Any ideas?

Here the design I am experimenting with: https://cad.onshape.com/documents/cace26656a717e831c8ca8ff/w/aa63b2eac792cde7392ff602/e/4c5477d04bbedb839dccd792?configuration=List_5jTWSIBKJ1DnCZ=Standard&amp;renderMode=0&amp;uiState=642c8d1bb05f15165c99ebca

fst

I think I found the answer: It is currently apparently not possible to reference other variables in function definitions.
So this works:
name: increment.  value: function(x){return x + 1};

But this doesn't:
name: startValue.  value: 42
name offsetFromStartValue.    value: function(x){return startValue+x;)
^^these two can still be defined, but #offsetFromStartValue(2.0) will fail

Thinking now about building a bigger (Featurescript)-feature that creates essentialy the entire part programmatically - might be easier.

--- old posting ---

I cannot get this to work. Have defined a function as value of a parameter as shown by @chadstoltzfus. Now I try to call it, but it is always shown as invalid.

Function definition: pipe_width_at: function(x){return pipe_height_at_bottom-(pipe_width_at_bottom-pipe_width_at_top)*pos/soundpipe_length;}

^^This still seems to work! (All variables inside this definition are defined above, they are lengths in mm. Couldn't define the function as length, it was accepted when I chose "any" though.)

Attempts to instantiate the function:
#pipe_width_at(#soundpipe_length+#soundhole_length)

#pipe_width_at(245mm)

#pipe_width_at(245)

^^ None of these seem to work.
Any ideas?

Removed link - not sure why my postings are not published when I post links to my public documents? Might have helped to understand the problem...

chadstoltzfus

@ferdinand_strixner
To my knowledge there isn't a way to reference Part Studio variables inside the scope of the lambda function, though it's worth noting you can send a Part Studio variable as an argument to the function.  

Ex: 
name: startValue.  value: 42
name offsetFromStartValue.    value: function(x, y){return y+x * in;)

Invoke #offsetFromStartValue(2in, #startValue)
Will return 44



Though you're probably right, it's going to be much more scalable and easy to manage to just make a custom feature.