[CMake] managing lists with space separated elements

[Bill Hoffman]

Piotr Dobrogost wrote:
> Bill Hoffman wrote:
> 
>> Piotr Dobrogost wrote:
>>> Bill Hoffman wrote:
>>>
>>>> There is no such thing as a list with spaces in CMake, that is a string.
>>>>  So, no there is no way to use the list command on strings directly. You
>>>> could use string(replace ) to do what you are trying to do.
>>> I've seen people already asking about this feature.
>>> Wouldn't that be useful to have this?
>>> I don't see any reason why not to support both kinds of commonly used
>>> lists instead of only one.
>>>
>>>
>> But, it is not a list....   Why not use string replace?
> 
> Because it is a list in its very nature. The fact we _can_ treat it as
> string doesn't change its inherent identity. That's even reflected when
> you name such variables. How would you name
> ${CMAKE_C_STANDARD_LIBRARIES} variable? It's a _list_ of some libraries.
> It's neither a set nor a graph nor a tree :) It's simply a list.
> 
> Every structure can be treated like a string because every structure can
> be serialized. But it doesn't help to understand this structure's
> inherent properties when we look at it mainly or only as a string. It
> doesn't help to manage such structure as well.
> 
> Take for an example a localization string. The main properties we are
> interested in are the language and maybe string's length. We don't
> usually do any operations on its words. And because of this it's _more_
> a string than a list. On the other hand we very often have to add/remove
> elements of variables like ${CMAKE_C_STANDARD_LIBRARIES}. And because of
> this it's _more_ a list than a string.
> 
> Bill, would you mind be so kind and show this topic to other people
> writing cmake in Kiteware? I'd like to know what they think about this.
> 
> I'd like to know what others on this list think about it as well. So if
> you're reading this post please tell us what you think.
> 
> 
The real solution is to use the list already in CMake.  It was a mistake 
to have CMAKE_CXX_FLAGS and CMAKE_C_STANDARD_LIBRARIES be strings they 
should have been lists.  If you want to convert a string to a list you 
can do it like this:

set(list ${string})

That will make the space separated list string into a ; separated list. 
  If you want to keep string a string you need quotes:
set(newstring "${string}").

Converting a list back into a string requires a foreach loop or a regex.

The problem is there are some variables in CMake which are currently 
strings that should be lists.  I don't think the solution is to add list 
operations for strings.  And you are right CMAKE_C_STANDARD_LIBRARIES 
should be a list.

-Bill