On 2/28/20 7:57 PM, aliak wrote:
I actually didn't realize it was a video, thought it was just an
article! - But anyway, it was just to point out that swift lowers to
specialized types when it comes to interpolation (which is what you and
adam are trying to get through). And therefor you can detect
interpolations being given to you and deal with them the way you want
and you can do a lot when you know you're getting an interpolation. You
can create types like
let example: SQLStatment = "select * from blah where a=\(a), b=\(b) ... "
I didn't get to this part of the video, but that is indeed pretty cool.
I'm assuming that this generates placeholders for the SQL statement and
attaches a and b as parameters?
However, D cannot do something like this exactly, because expressions
define the tuple, not how they are used.
But this is possible (with the proposed DIP or ours):
alias sql = "select * from blah where a=$a, b=$b"; // aliased to the tuple
connection.query(sql);
a = 5;
connection.query(sql); // another query with `a` set to 5 now.
Swift can do some pretty cool things due to the type resolver, but it
comes at a cost (some expressions that are trivial in D make the
compiler complain about them taking too long to resolve).
I also didn't realize the takeaway would be that swift does appending
😆- which by the way, is not completely accurate. And it does not
generate temporaries (unless you mean passing in parameters? There's no
way around that if you want to end up with a string based on runtime
values - it'll have to be processed in to a string somewhere).
For example, the part where they change the date formatting, they use a
date formatter to generate a string for the date, which then is appended
to the string interpolation.
Yes, you need to allocate a string. But you should only allocate one.
You can also get an interpolated string directly in to "print
processing" if you wanted to: https://swift.godbolt.org/z/muAzgm
Hm... I'm not too impressed with this when compared to writefln(i"hello
$("hello"), $x"); which works without such extra mechanics or strange
call syntax.
When it comes to printing it really doesn't matter if you construct a
string on the stack and pass it along. You're IO bound anyway.
IO is not usually processed directly to the device. Usually it's
buffered. Writing directly to the buffer is preferable to generating a
string on the stack, and just copying that to the buffer.
One very interesting thing of note is the way they combine named
arguments with string interpolations.
Yeah, that part is cool. But that comes for free with Swift. Potentially
with the right additions to the named parameters DIP, it would be
feasible to do something similar with this DIP.
Also another note, this tuple expansion should really not be called
string interpolation, since it does not result in a string :/ It's more
string expansion really.
I recommended calling it a "formatted tuple" to avoid conflation with
existing string interpolation implementations.
-Steve
