The state of string interpolation
couteaubleu at gmail.com
Mon Dec 10 13:48:58 UTC 2018
On Thursday, 6 December 2018 at 16:19:12 UTC, Steven
> With the concept of lowering to a tuple, I'd love to use such a
> thing for database queries.
> For instance:
> db.exec("UPDATE Foo SET a = ?, b = ?, c = ?, d = ? WHERE id =
> ?", aval, bval, cval, dval, id);
> db.exec(i"UPDATE Foo SET a = $aval, b = $bval, c = $cval, d =
> $dval WHERE id = $id");
I really like that, but I'd add a caveat: this syntax makes it
harder for db.exec to know which arguments you give it are
trusted compile-time inputs, and which arguments are unsafe
I'd argue for a second syntax to be added as well, fi"formatted
db.exec(fi"UPDATE Foo SET a = $aval, b = $bval, c = $cval, WHERE
id = $id");
would lower to:
db.exec("UPDATE Foo SET a = %s, b = %s, c = %s, WHERE id = %s",
aval, bval, cval, id);
That way, db.exec would be able to interpret its first argument
as trusted input and everything else as unsafe.
That syntax might be redundant if a builtin FromInterpolation
struct is created. The thing is, there have been arguments
against using a builtin struct, and a db.exec method built for
interpolation would be incompatible with regular use, so this:
db.exec("UPDATE Foo SET a = ",aval,", b = ",bval,", c = ",cval,",
WHERE id = ",id);
would not work, which would have to be documented, etc.
On the other hand, a fi"some string with $var" syntax could
leverage any already existing db.exec method with a "C format"
first parameter (including actual C functions?), without forcing
the library implementation to differentiate between normal
arguments and FromInterpolation arguments.
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