On Wednesday, 19 April 2017 at 13:04:08 UTC, Jonathan Marler
wrote:
On Wednesday, 19 April 2017 at 12:03:47 UTC, Stefan Koch wrote:
On Wednesday, 19 April 2017 at 11:59:51 UTC, Jonas Drewsen
wrote:
I can think of 3 reasons.
1. Requires GC.
NOTE: I believe that most applcations should use GC memory,
that being said, library code has to be nogc wherever it can if
it wants to be used by nogc apps, so this solution is unusable
in alot of library code.
2. It's verbose. Jonas provided a good example of why and he
makes a good point that your example only has 1 formatted
argument and this problem gets much worse with multiple.
3. The biggest reason I wouldn't use this solution because it
uses string composition. String composition wastes memory and
memory management cycles. And when I say "waste" what I mean
is, the use is unnecessary. In general composition is a
powerful tool because it allows you to easily overload and
abstract and add new functionality, however, it requires
runtime overhead. This is the reason that the
toString(delegate) was created to replace the composable
toString paradigm. It's also the reason that string formatting
exists at all.
To summarize:
// requires GC, too verbose, uses string composition which
wastes heap resources
writeln("The date is " ~ format("%04d", year));
// efficient, but format string and args can get out of sync.
writefln("the date is %04d", year);
//
writefln($"the date is {year:04d}");
If string interpolation gets reduced to the 2nd case, then it
will have the same efficiency and solve a problem. Whether
that problem justifies the change is up for debate, but I think
it *might be*.
As a string interpolation sceptic I have to admit that I found
one application of that concept that is probably much better than
the current C derived format strings: Internationalisation.
dates["en"] = "The date is %2$02d-%1$02d-%3$04d";
dates["fr"] = "La date est %1$02d-%2$02d-%3$04d";
writeln(format(dates[lan], day, month, year));
with interpolation we have
dates["en"] = $"The date is
{month:%02d}-{day:02d}-{year:04d}";
dates["fr"] = $"La date est
{day:%02d}/{month:%02d}/{year:04d}";
which is a little bit easier to read than positional format
specifiers, which have the added backdraw (at least in C, I don't
know for D) that they are an none or ALL thing. When you need
them, you have to put them an all format specifiers.
This said, the interpolation has in that case a big drawback,
i.e. that they "export" the variable names outside of the scope
they are defined in. That's a thing that is often required for
I10N, that the strings are defined in a separate file or module
and selectively imported (at runtime).
