Questions about include statements

Yet more newbie questions: I'm lovin' OpenSCAD and have progressed from single parts, through simple assemblies, and now I am attempting a complex assembly with multiple dependencies and I'm having trouble.  So, I'm stepping back to create an organized structure and a set of best practices.

I develop each part in its own file which contains the part's module, dimensional constants, and functions for computed values. My top level assembly file references all of the part files using include statements and puts it all together.

1. My first question is about include statements:  How do I conditionally "include" library files?

Each part and the assembly needs a common library, for example, metric_screws.scad. As I develop each part, each part file needs to have a "include <metric_screws.scad>;".  

The top level assembly includes metric_screws.scad, which then gets included again as each part file is included.

So, how do I avoid these multiple includes of the same librry from the top-level assembly?  Or, how do I conditionally execute include statements in the part files?

2. When would you use a "use" statement rather than an "include" statement?

Thanks

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You can't conditionally include files so I do end up with the same file included over and over again. 

The best I can do is to only put constants I need to make global in my include files and a use of a second file that has all the functions and modules. Used files are cached and only parsed once. For example I have a screws.scad that I include and it uses screw.scad.

On Sat, 17 Apr 2021 at 15:36, LenStruttmann <[hidden email]> wrote:

Yet more newbie questions: I'm lovin' OpenSCAD and have progressed from single parts, through simple assemblies, and now I am attempting a complex assembly with multiple dependencies and I'm having trouble.  So, I'm stepping back to create an organized structure and a set of best practices.

I develop each part in its own file which contains the part's module, dimensional constants, and functions for computed values. My top level assembly file references all of the part files using include statements and puts it all together.

1. My first question is about include statements:  How do I conditionally "include" library files?

Each part and the assembly needs a common library, for example, metric_screws.scad. As I develop each part, each part file needs to have a "include <metric_screws.scad>;".  

The top level assembly includes metric_screws.scad, which then gets included again as each part file is included.

So, how do I avoid these multiple includes of the same librry from the top-level assembly?  Or, how do I conditionally execute include statements in the part files?

2. When would you use a "use" statement rather than an "include" statement?

Thanks

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You can define the same function or module multiple times.  Later definitions replace earlier ones.  So including the same file repeatedly doesn't break anything.   Even definitions of global constants are just replaced if they happen in include files.

That's good to know.  I still find it odd.  If my assembly and my parts all include:

include <BOSL2/std.scad>;
include <BOSL2/metric_screws.scad>;

... it seems to me that there would be a performance hit to re-read those files for each part.  Then again, after the first file read the OS will have all (or most) of the file contents cached. I suppose I'm just showing my age, coming from a programming background where file reads were enormously expensive.  I guess that this behavior is not much different from a C compiler including .h files.

Be aware if you use "use" that any variable assignments at the top level will be executed any time you call a function in your file, which can result in huge slow downs if you call functions a lot and have something slow to compute in those top level assignments.

Thanks!  These are the types of performance hits I'd like to avoid.

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So, would a "best practice" be:

(1) Assuming that libraries are well-designed with a minimum number of  instantiated variables,
(2) Part files include any libraries they need, but never instantiate global variables. Instead, they expose all values only via functions.
(3) The top level assembly only "use"s part files, accessing everything as a module or a function.

?

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Yes but that would mean wrapping all my objects with functions.

The problem remains with complex machines that  their used files need variables to calculate positions, etc. If you wrap all those expressions in functions you end up with an exploding tree of function calls. 

On Sat, 17 Apr 2021 at 22:49, LenStruttmann <[hidden email]> wrote:

So, would a "best practice" be:

(1) Assuming that libraries are well-designed with a minimum number of  instantiated variables,
(2) Part files include any libraries they need, but never instantiate global variables. Instead, they expose all values only via functions.
(3) The top level assembly only "use"s part files, accessing everything as a module or a function.

?

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Have we thought of adding some smarts to evaluation?

Only expressions with $variables can change, but could cascade,

 

a=$b*2;

c=a/$d;

e=max(c,$f);

g=w*h;

 

Build a dependency tree;

 a {$b}, c {a, $d}, e {c, $f}, g {w, h};

once you hit EOF you could optimise the tree for reading;

 a {$b} c {$b, $d} e ($f) [remove g or discard earlier]

First simple test could be only re-evaluate (all) expressions with a $variable in its tree hierarchy, ie the optimised list.

 

Second you could cache the last value of the $variable in the tree, if it has changed since last time re-evaluate the relevant branch.

 

?

 

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From: nop head [mailto:[hidden email]]
Sent: Sun, 18 Apr 2021 06:44
To: OpenSCAD general discussion
Subject: [OpenSCAD] Re: Questions about include statements

 

To be clear I generally avoid including the same file twice in the same scope but screws for example are included in most sub assemblies that are themselves used, so they get included into multiple scopes as each used file has its own variables.

 

The fact that variables are evaluated when a module of function in a used file is called really slows down my builds and I think sets a finite limit to the complexity of the design. I am struggling with my latest 3D printed. I don't think I could model a car or an airliner in OpenSCAD. The time to instantiate the variables would tend towards infinity. It already takes minutes.

 

For most of my designs that only have one main file or perhaps two or three it isn't a problem but when there are 30 files it gets very slow. I think 100 would be impossible, whereas a C++ program with 100 files in it is not really a problem. There isn't really a limit because compile time is linear with the number of files, whereas with OpenSCAD it increases exponentially.

 

On Sat, 17 Apr 2021 at 20:32, LenStruttmann <[hidden email]> wrote:

You can define the same function or module multiple times.  Later definitions replace earlier ones.  So including the same file repeatedly doesn't break anything.   Even definitions of global constants are just replaced if they happen in include files.

That's good to know.  I still find it odd.  If my assembly and my parts all include:

include <BOSL2/std.scad>;
include <BOSL2/metric_screws.scad>;

... it seems to me that there would be a performance hit to re-read those files for each part.  Then again, after the first file read the OS will have all (or most) of the file contents cached. I suppose I'm just showing my age, coming from a programming background where file reads were enormously expensive.  I guess that this behavior is not much different from a C compiler including .h files.

Be aware if you use "use" that any variable assignments at the top level will be executed any time you call a function in your file, which can result in huge slow downs if you call functions a lot and have something slow to compute in those top level assignments.

Thanks!  These are the types of performance hits I'd like to avoid.

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Thanks, everyone for this discussion. It has very much helped with my understanding of "include".

But, I'm still unclear on the purpose of the "use" statement.  I guess that there are only special cases where the "use" statement is appropriate.

Even files that only contain functions and modules aren't always compatible with "use".  For example, <BOSL2/metric_screws.scad> only contains functions and modules.  Yet, you must "include" it, presumably because it includes other files.

So, back to my original question: I now know that:

(1) Having multiple "includes" of the same library file is not bad and there is usually not much of a performance hit.
(2) I don't need to "include" a library in my assembly if that library is included within a part file that the assembly includes.  

Thanks!

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