Let me clarify the requirements and rephrase the question --
REQUIREMENTS
`assert`, `enforce` and the `unless` function I wrote (above) all
allow the condition to be expressed in an affirmative sense, and
they also achieve the goal of readability. These are the initial
requirements.
`unless` improves on `assert` and `enforce` by allowing a custom
action to be specified. This might be to write an error message
and exit (like `assert` and `enforce`). But it could also be to
write a warning message (to console or a log file) but not exit.
So the next requirement is to be able to specify a custom action.
Unfortunately a function, like the one I wrote, doesn't work
because it doesn't allow actions that would skip or repeat some
code (`continue`, `goto`, etc) to be specified as the second
argument. It also doesn't allow code to be skipped or repeated
after executing the function in the second argument. (That is,
after writing a warning message or log notice, continue
processing at some point.) A conditional operator like `if` is
needed, not a function.
THE ESSENTIAL QUESTION
Is there a way to write an `unless` operator that would allow the
condition to be expressed in an affirmative sense? It would be
used like `if`, i.e. something like:
unless ( <condition> ) {
<handle it>; // Or even: <ignore it>
continue; }
Templates offer a clean syntax, but I can't come up with a way to
use them for a conditional operator. Mixins are flexibile, but I
suspect the result would not be very readabile (that is, less
readable even than "if ( ! (..." ). I was hoping that some
feature, or combination of features, in D might allow this to be
achieved.
