Switch statement

john_mcclary

Is there an equivalent way of doing switch statements in FS?

instead of a bunch of if-else statements

konstantin_shiriazdanov

I would happily use "switch" too if it was there.

ilya_baran

There are indeed cases when a switch statement makes things simpler, but in this case, you could get a similar effect by doing:

const table = {<br>&nbsp;...<br>&nbsp; &nbsp;3/4 : { KeySeat : .644, KeyWay : .837},<br>&nbsp;13/16 : { KeySeat : .708, KeyWay : .900},<br>&nbsp;...<br>};<br>var entry = table[ShaftDia];<br>if (entry == undefined)<br>&nbsp; &nbsp;throw "No match for shaft diameter: " ~ ShaftDia;<br>var KeySeat = entry.KeySeat;<br>var KeyWay&nbsp;= entry.KeyWay;<br>

Jake_Rosenfeld

@mbartlett21

The switch expression does not support a default, but you can check if none of the cases were hit by checking if the switch returned `undefined`, and then doing whatever default behavior you want (similar to what Ilya does above in his map example).

konstantin_shiriazdanov

I would happily use "switch" too if it was there.

Jake_Rosenfeld

@john_mcclary @konstantin_shiriazdanov

@ilya_baran informs me that there is a switch-expression in FS that we may document for public use in the future.  It is slightly different from a switch-statement in that it does not switch on an expression and then execute a block of code (a statement), but rather switches on an expression and then return another specified expression.  This can be made to act like a traditional switch statement using lambdas if desired.

Here is an example:
https://cad.onshape.com/documents/f6780441494046f4439a8219/w/71e7c5c95c521d8716fa75fa/e/631535138fdaba3ef7928ea2

konstantin_shiriazdanov

@Jake_Rosenfeld so this switch is a function, I beleve Ilya wrote it half an hour ago)

john_mcclary

@Jake_Rosenfeld well I suppose that is similar to a switch statement, but it doesn't allow flow through multiple cases, and it still requires many lines of code.

y = 3;<br>switch(x)<br>{<br>case 0: y++;<br>case 1: y++;<br>case 2: y++; break;<br>case 3: y = 10; break;<br>default: y = 0;<br>}<br><br>X = 0 -> Y = 6;
X = 1 -> Y = 5;
X = 2 -> Y = 4;
X = 3 -> Y = 10;
X = 4 -> Y = 0;

Not that I end up using that method very often, but it is a traditional syntax for switch which I have taken advantage of before.

What brought this on was I had a long list of if-else statements to fill in all the keyway sizes given a shaft diameter.
it ended up being 500 lines of code that is ugly to read.
if they were switch statements it would only be around 100 or so lines of code and resemble a readable table.



Vrs:

case 7/8: KeySeat = .771; KeyWay = .900; break;
case 15/16: KeySeat = .796; KeyWay = 1.051; break;
case 1: KeySeat = .859; KeyWay = 1.114; break;

ilya_baran

There are indeed cases when a switch statement makes things simpler, but in this case, you could get a similar effect by doing:

const table = {<br>&nbsp;...<br>&nbsp; &nbsp;3/4 : { KeySeat : .644, KeyWay : .837},<br>&nbsp;13/16 : { KeySeat : .708, KeyWay : .900},<br>&nbsp;...<br>};<br>var entry = table[ShaftDia];<br>if (entry == undefined)<br>&nbsp; &nbsp;throw "No match for shaft diameter: " ~ ShaftDia;<br>var KeySeat = entry.KeySeat;<br>var KeyWay&nbsp;= entry.KeyWay;<br>

john_mcclary

Thanks @ilya_baran That's what I'm looking for for this use case

john_mcclary

Went from 465 lines of code down to 189 with that

I'll know better next time

MBartlett21

@Jake_Rosenfeld
Can you specify a default with that switch statement?

john_mcclary

think that is what the if(entry == undefined) is doing

Jake_Rosenfeld

@mbartlett21

The switch expression does not support a default, but you can check if none of the cases were hit by checking if the switch returned `undefined`, and then doing whatever default behavior you want (similar to what Ilya does above in his map example).

Chris_D_Mentes_001

Switch no longer seems to work unfortunitally, look forward to seeing it in the future tho

MBartlett21

@Chris_D_Mentes_001

What do you mean? Onshape uses it many times in their own code and we can create code just like it:

Chris_D_Mentes_001

Ah okay thanks for this I've been using it wrong.