This is the definition of "filter" function, and I think it called itself within its definition. I'm guessing how it works?
'''D
template filter(alias predicate)
if (is(typeof(unaryFun!predicate)))
{
/**
Params:
range = An $(REF_ALTTEXT input range, isInputRange, std,range,primitives)
of elements
Returns:
A range containing only elements x
in range
for
which predicate(x)
returns true
.
*/
auto filter(Range)(Range range) if (isInputRange!(Unqual!Range))
{
return FilterResult!(unaryFun!predicate, Range)(range);
}
}
'''
I think this line needs explanation:
'''D
return FilterResult!(unaryFun!predicate, Range)(range);
'''