Re: [Boost-build] Explanation of word "grist" in documentation

Subject: Re: [Boost-build] Explanation of word "grist" in documentation
From: Edward Diener (eldiener_at_[hidden])
Date: 2016-05-25 17:36:08

On 5/23/2016 8:39 PM, aaron_at_[hidden] wrote:
>> I follow your example but I don't follow the notion of "grist" in
>> general. I don't see what it is about 'static' that relates to
>> "filename-related components".
>
> Actually,  "static" doesn't relate to "filename-related components" at all.
>
> ---
>
> What that part of the documentation is saying is that you can
> perform operations on the values of the variable assuming the value
> contains a grist or a path-like. The operation performed is dependent
> upon the modifier used.
>
> For example, if I wanted to see which features were in the variable "x"
> I could use the :G modifier to do the following
>
> # create my list of properties
> local x = <toolset>gcc <link>static ;
> echo $(x:G) ;
> # will ouput: <toolset> <link>
>
> Likewise, if I wanted to see only the values of the properties, I could use
> the ":G=" modifier (which allows me to set the "grist" to whatever value
> comes after the "=", in this case, I'm setting it to the empty string):
>
> local x = <toolset>gcc <link>static ;
> echo $(x:G=) ;
> # will output: gcc static
>
> Note: I would only use the above modifiers if I knew that all of the
> value(s)
> in my variable were properties.
>
> It's also possible to use the other modifiers when you know that the
> value(s)
> in the variable are paths or path-like. For example,
>
> local x = path/to/some/file.cpp ;
> # if I wanted to get the parent directory, I could use the :P modifier
> echo $(x:P) ;
> # outputs: path/to/some
>
> # if I wanted to get the base name (no path and no extension), I could
> # use the :B modifier
> echo $(x:B) ;
> # outputs: file
>
> Whenever I need to play around with the Jam language, I will throw some
> statements at the top of my Jamroot (like the examples above) followed by
> "exit" rule. For example:
>
> local x = a b c ;
> local y = 1 2 3 ;
> echo $(x)$(y) ;
> exit ;  # exit here so that nothing builds
>
> Hopefully that helps,

I am pretty sure that "grist" means the part of any value surrounded by 
angle brackets ( '<' and '>' ). Unfortunately the documentation never 
explains that. I concluded that by looking at a utility.jam rule called 
'ungrist' and looking at the comment for that rule.