Re: [jamboost] [iostreams] Need help understanding the Jam language

From: Rene Rivera (grafik.list_at_[hidden])
Date: 2005-06-04 16:51:39

Jonathan Turkanis wrote:

> Among other thing, I realized I don't really know how to return a value from a
> Jam rule.
[...]
> I just discovered that the return statement does not seem to prevent control
> from continuing past the "if" block to the line marked "...".
[...]
> I really have no idea what's going on here.

It's simple ;-) "return 1 ;" sets the return value to the strings ["1"] 
(all values Jam are string lists). When the rule finishes, by getting to 
the last statement, the return value is passed back to the caller. So this:

rule x ( )
{
if $(_X_)
{
return 1 ;
}
else
{
return 2 ;
}
}

Is equivalent to... in C++:

std::vector<std::string> x()
{
std::vector<std::string> r;
if ( _X_.size() > 0 )
{
r.assign(1,"1");
}
else
{
r.assign(1,"2");
}
return r;
}

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