Troberg wrote

Hmmm... if you set a variable named center to anything but true, it defaults
to false.
And it doesn't seem to cause a problem with a module named center.

translate([20,20,20])
center();

module center(){
sphere(10);
}

center = true;
cube(10,center);

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lar3ry wrote

Still, it's not a nice way of doing it. At the very least, prefix such
pre-defined constants, for example scadcenter, which will both reduce the
risk of namespace clashes and clearly show what's a predefined constant.

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lar3ry wrote

I'd say that's a confusing way to put it.  (I couldn't quite figure out what
you meant.)

A default is something that happens when data is missing, but if you pass a
value to center then there is no missing data, so the default doesn't have
obvious relevance.  However, it seems that the behavior of the cube module
is that if center=true then you get a centered cube.  And if center is
anything else, you get an uncentered cube.  This is arguably a bug.  One
would expect that anything which tested as true should cause the cube to be
centered.  (That is, [3,4] is true in a boolean context, but acts like false
when given as the center argument to cube().)  Or perhaps you should get an
error message if a non-boolean value is passed to center.

But I think Troberg's point is that he likes to use "center" as a variable,
which conflicts with this approach, and conflicts with your original idea of
being able to write "center" instead of "center=true" when specifying a
centered cube.

It might for example be natural to define the center of some component, so

center=[3,4,5];

This will conflict with "center=true" and will cause cubes that were
supposed to be centered come out not centered if you've got invocations of
cube(size,center) with the intention that this produce a centered cube.

If I saw some code that had stuff like

cube(size,center);

in it then I'd wonder what the value of center was.  It doesn't read as
"centered cube" to me.  And the goal is just to avoid typing "=true"?  I
suggest that if you're so offended by the need to type "center=true" and you
have a lot of centered cubes, the answer is to make a centered cube module:

module center_cube(size) { cube(size,center=true);}

You can make similar pass-through modules for other things you want to have
centered.  You can give it a shorter (more cryptic) name if you're really
frustrated by all the typing.  I suppose also if the goal is brevity you
can do "cube(1,true)".

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adrianv wrote

Well, I said default, because anything other than true acts the same way a
false acts.

Let me ask you a question. If I want a sphere that is not centered, why
can't I write sphere(10,center = false);? Is there ANY object that is
centered that could be made not centered by using center = false?
It isn't so much the typing. It's more like I don't see a need to ever use
center = false.

You can make similar pass-through modules for other things you want to have
centered.  You can give it a shorter (more cryptic) name if you're really
frustrated by all the typing.  I suppose also if the goal is brevity you
can do "cube(1,true)".

I could, but false by itself is less "self-documenting" than center = true,
or even just center, if it would be a parameter that ALWAYS evaluated as
true in the parameters of an object that allowed center.

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