Given this little program testing regexs, I decided to replace
one of the example's assert with an enforce:
--------
import std.regex;
import std.exception;
void main()
{
auto m = match("hello world", regex("world"));
assert(m);
enforce(m); // <-- HERE
enforce(cast(bool)m);
enforce(!m.empty);
}
--------
I get the compile errors:
src\phobos\std\exception.d(356): Error: pure function 'enforce'
cannot call impure function '~this'
src\phobos\std\exception.d(358): Error: pure function 'enforce'
cannot call impure function 'opCast'
While I understand the problem at play, I have a few doubts:
1)Why the difference between assert and enforce? Shouldn't both
have the same restraints?
2)What exactly does purity mean for a *member* function?
3)And shouldn't RegexMatch's .opCast (and .empty) should be
qualified as pure?
...
I did some digging while typing, and was about to suggest that
the problem could be solved if enforce was required to take a
boolean as an argument (makes sense), forcing the cast *outside*
of the enforce. However, it would appear that enforce returns its
value, the goal (probably) being to make this legal:
auto bar = enforce(foo());
The return value is enforced and passed to bar in a 1-liner.
BUT... assert doesn't do that. THAT is the original source of the
difference in behavior.
So I'll rephrase my 1):
Why the difference in behavior regarding the return value? Is it
just historical/no real reason, or is there something for me to
learn here?
