Re: [Boost-build] Using variable modifiers problem

Subject: Re: [Boost-build] Using variable modifiers problem
From: Steven Watanabe (watanabesj_at_[hidden])
Date: 2017-02-19 18:49:19

AMDG

On 02/19/2017 11:40 AM, Edward Diener via Boost-build wrote:
> I seem to be missing some aspect of variable modifiers. In
> http://www.boost.org/build/doc/html/jam/language.html#jam.language.variables
> 
> it gives tells me that variable modifiers must be in the form of $(vm),
> where v is the variable name and m is the modifier. Yet in feature.jam I
> see this code:
> 
> rule values ( feature )
> {
>     return $($(:E=:G=$(feature)).values) ;
> }
> 
> and I do not understand how it can be syntactically correct since the :E
> does not follow a variable name AFAICS. Clearly I am missing how such an
> expression is being parsed.
> 

The variable name in this case is the empty string.

> This is not a vain inquiry. I am trying to determine why some code is
> failing when a call to feature.values with a particular parameter is
> returning an empty result, but I cannot do so unless I understand what
> is happening in the above jam code.
> 

The purpose of $(:E=:G=$(feature)) is to wrap $(feature)
with <>.

In Christ,
Steven Watanabe