On Saturday, 29 February 2020 at 14:41:16 UTC, Steven
Schveighoffer wrote:
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?
I'm not sure if it's in the video (I haven't seen the video). But
it was just an example, implementations would vary I'd assume.
Here's one from a quick search for e.g.:
https://github.com/groue/GRDB.swift/blob/4c8574aa4c08ff715ce0e63b38502ac1e8529069/GRDB/Core/SQLInterpolation.swift
However, D cannot do something like this exactly, because
expressions define the tuple, not how they are used.
Yep, and similarly expressions define the interpolation pattern
in swift, not how they are used as well. So the tuple thing is
also pretty sweet! I'd imaging you'd be able to do something like:
auto sql = SQLStatment(i"select * from blah where a=$a, b=$b");
where
struct SQLStatement {
string formatted;
// What template magic is needed here? This is where I get a
little worried.
this(S : _interpolated_object!Specs, Specs, Args...)(S s, Args
args) {
// build formatted...?
}
alias formatter this;
}
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.
Yeah, and that's pretty sweet too!
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).
Yeah, swift ha a few problems with its type solver during
semantic I think.
let a: Double = -(1 + 2) + -(3 + 4) + -(5)
Will fail to compile on my machine, and you need to break it up.
But, on the other hand, swift's constraint solver avoids
backwards situations like:
void f(bool) { "bool".writeln; }
void f(int) { "int".writeln; }
enum A { one }
void main() {
f(0);
f(A.one);
}
And:
void main() {
struct B {
B opBinary(string op : "+")(int b) { return this; }
}
static if (is(typeof(B.init + size_t.init))) {
size_t x = 1;
B b1, b2;
b1 = b2 + x; // fails here
}
}
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.
Generating temporaries is not a constraint that the interpolation
system puts on you.
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.
Indeed.
