On 2019-01-16 06:32, Walter Bright wrote:
You deliberately wrote that, and I'm confident you'd never try to pass
that off as good work.
Yes. I'm showing it's possible to write bad code in all programming
languages with all (most) features. Macros are not required for that.
With macros, however, programmers are convinced they are creating models
of clarity. I've seen programmers truly believe:
#define BEGIN {
#define END }
improves their C code. Fortunately, that was ridiculed out of existence
in the 1980s, but the more subtle abuses persist with their ardent
defenders. I used to use a lot of macros in my C code, and a few years
back made an effort to remove them all from the dmd source code. The
result was very satisfactory.
I've seen entire code bases abandoned because of macros after the
original developer left.
D has done a great job of replacing the C preprocessor with alternative
features. These include: "import", "debug" and "version". These features
are great and don't need much improvement. They take care of the stuff
that is really difficult to avoid the preprocessor in C for.
Then we have the other stuff: macros. To insert code at the
instantiation point. For this, D has string mixins and template mixins.
This is where D is lacking some features. For example, it's not possible
to insert a symbol with a string mixin that the surrounding scope at the
instantiation point cannot access. For example, you want to insert two
symbols, but the surrounding code should only have access to one of the
symbols, the other one is a helper symbol to the first one. This is not
possible today. Unfortunately that doesn't stop anyone from trying to
come up with there own workarounds and solutions, like generating some
obfuscated symbol name. It's not gonna make it less accessible, just
less likely to collide with an existing symbol.
It's also not possible to insert a symbol that refers to another symbol
in another module without risking a symbol conflict in the local scope.
There's a word for this, mixins are not hygienic.
While D improves a lot on the C preprocessor it didn't reach all the way
to cross the finish line.
--
/Jacob Carlborg
