Difficulty with defining a volume parameter

Matthew_Wilson

I'm writing a feature that takes a volume measurement from the user.  I'm running into trouble with the isVolume predicate:

FeatureScript 1821;
import(path : "onshape/std/geometry.fs", version : "1821.0");

annotation { "Feature Type Name" : "My Feature" }
export const myFeature = defineFeature(function(context is Context, id is Id, definition is map)
    precondition
    {
        // Define the parameters of the feature type
        annotation { "Name" : "My Volume" }
        isVolume(definition.myVolume, VOLUME_BOUNDS);
        
    }
    {
        // Define the function's action
    });

The volume definition throws the warning: "Expected parameter id to be defined as a field on val"  I have zero idea what that means.  I don't think that I'm using it wrong, it's documented here: https://cad.onshape.com/FsDoc/library.html#isVolume--VolumeBoundSpec  This is just the same as a Length definition, what am I missing?

kevin_o_toole_1

There is currently no "volume parameter" UI for that syntax to map onto. If we supported it, I'd bet our syntax would match your snippet, but we don't support it yet.

If you want to input a volume, two possible workarounds are:

1. Input a plain real number, interpret it in your code as e.g. in^3
   
2. Input an isAnything() parameter, have the user manually type the value and units e.g. 3 in^3 into that input

Jacob_Corder

You could also have an enum for volume units that you want to use. input a number and another input, its units. then convert it in your code to a ValueWithUnits.
 

Matthew_Wilson

Thanks Kevin and Jacob!  I did end up using isReal and converting it to mm^3.  It's just a quick and dirty FS for now so that works out.  I like the isAnything, I could then at least validate the input and allow other units.

I was confused because the docs seem to indicate that you can use isVolume in this way.  Maybe we can get an improvement request to add a volume parameter to the UI? ;-)