Hello Nick,
"John Reimer" <terminal.n...@gmail.com> wrote in message
news:28b70f8cfcfe8cb30c0a0e2a...@news.digitalmars.com...
Hello Sean,
bearophile wrote:
Walter Bright:
Excess isn't the problem, I want to see if import cycles is.
Generally all the modules in my dlibs import each other. This is
nearly unavoidable, if a module contains string functions, and
another one contains math stuff, the string module will want to use
some math stuff and the math module may need string representations
and processing. In the D specs I haven't seen an advice to not use
cyclic imports, so I don't want such compiler flag, I prefer a
compiler able to manage such cyclic imports efficiently.
Cyclic imports are a bad idea in general because of the impact they
have on verifiability (unit testing). But as you say, sometimes
they're unavoidable.
Sean
I'd going to wager that they are /often/ unavoidable, especially in
ported projects from other languages that have either no concept or a
different concept of modules/packages.
DWT is perhaps the single worse example of cyclic imports. I'm not
sure
how the design could have been improved in Java's SWT. All it takes
is
the need to reference one symbol in each module (because each object
apparently needs to just "know" about the other) to create a cyclic
import
issue in D.
Static initialization has also been a problem in DWT such that a few
significant workarounds were necessary.
I agree that the interdepencies should be avoided in all new projects
designed specifically for D. I'm just not sure what the solution
would be for the great mass of ported software.
-JJR
This might be a naive idea, and wouldn't solve the problems with
cyclic dependancies in the general case: But regarding the static
initializaton issue (which I've come up against myself), what if
static initializers allowed some sort of clause like this:
module foo;
import bar;
// Exact syntax not really important right now
this() dependsOn(bar) {
// Do some initing that depends on
// bar's static initializer having been run.
}
That would force foo's static initialization to be run sometime after
bar's. Obviously, any cycles in the graph of "dependsOn"s would be an
error.
Some sort of explicit ordering would likely be a solution. It would be /really/
nice if their were a clean way of implementing this... but it's really hard
to say how it should be done. I'm not sure how it is done (if at all) in
other languages that implement a similar feature.
All I know is that, static initializations become almost useless at worst
and extremely problematic at best in large projects, especially object based
ones. There are workarounds, of course. One ends up having to learn not
to be too dependent on this D feature.
-JJR
