[CMake] lexical scoping

Ken Martin ken.martin at kitware.com
Fri Nov 2 14:26:21 EDT 2007

Variables can be a PITA :) They have unusual scoping, mixed documentation,
etc. In CVS there have been some changes. We have extended the concept of
properties which are scoped to an object (source file, target, directory,
global, test, for example) and are documented, can be inherited, and can be
tested to verify they are documented. This is nice and meets some needs of
CMake. But ... there are still variables.  Recently Bill and I have started
documenting variables in the source code (cmake --help-variables works) such
that you can get documentation on supported variables in cmake. These
documented variables are the ones we will try to keep backwards compatible
(tm), all others are up in the air.

But to the question at hand...adding scope to variables. Variables have
scope right now of

1) the CMakeListfile they are defined in
2) any included files that are included after the variable is set
3) and subdirectories of the directory they were defined in and processed
after the setting of the variable
4) they can be access globally using get_directory_property and specifying
the directory etc

the macro command is like a cpp macro so scoping does not make a lot of
sense for it. What would/could make sense is a function command that creates
a function. (think of the difference in a macro versus a function in c,
macros have no inherent scope they are just string replacements, functions
do have scope built in). With a function command we could probably figure
out some way to create variables that are scoped to the function only. Most
of the places we are using macros really could/should be functions. My main
question would be if we had a function, how would you want variables

1) all set commands create "local" variables to the function (a mess for
functions that do an include of other cmake code)
2) a special set command or signature that creates a local variable scoped
to the current function
3) a mode to switch the behavior of set (yuck)
4) something else


Ken Martin PhD 
Kitware Inc.
28 Corporate Drive
Clifton Park NY 12065
518 371 3971 

> -----Original Message-----
> From: cmake-bounces+ken.martin=kitware.com at cmake.org 
> [mailto:cmake-bounces+ken.martin=kitware.com at cmake.org] On 
> Behalf Of KSpam
> Sent: Friday, November 02, 2007 1:32 PM
> To: cmake at cmake.org
> Subject: Re: [CMake] lexical scoping
> On Friday 02 November 2007 09:54:51 Brandon Van Every wrote:
> > Is it feasible to modify the CMake language to have lexical scoping?
> I agree.  The lack of variable scoping is currently my 
> biggest annoyance with 
> custom macros.  Additionally, I believe that custom macros 
> are pretty much 
> required for any mid to large scale project.  Life in the 
> CMake scripting 
> language would be so much nicer if we could scope variables 
> at the macro 
> and/or file level.
> Justin
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> CMake at cmake.org
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