On Wednesday, 28 January 2026 at 09:53:45 UTC, Lars Johansson
wrote:
In general programming with D has been a pleasent experience.
BUT templates, I do not get it. Instead of having well defined
types, it seems you can have anyting with as!.
Consider `java/sql`, querying a `ResultSet`...you'd use
`.getInt`, `.getString`, `.getFloat`, `.getDouble`...for
`d2sqlite3`, it's `as!int`, `as!string`, `as!float`, `as!double`.
And how do I know I should use e.g. 'as!quirky' in some special
case?
Or are there a small set of well defined as! along with the
types?
From a brief look at the source code, it seems like there are
constraints:
```dlang
auto as(T)(T defaultValue = T.init)
if (isBoolean!T || isNumeric!T || isSomeString!T)
```
This gives you an indication of what kind of values `T` can be.
If you wanted to deal with the whole row, you can also provide
your own struct:
```dlang
T as(T)()
if (is(T == struct))
```
From the unittest:
```dlang
unittest
{
struct Item
{
int _id;
string name;
}
auto db = Database(":memory:");
db.run("CREATE TABLE items (name TEXT);
INSERT INTO items VALUES ('Light bulb')");
auto results = db.execute("SELECT rowid AS id, name FROM
items");
auto row = results.front;
auto thing = row.as!Item();
assert(thing == Item(1, "Light bulb"));
}
```
Generally, I find templates useful, although a little bit of a
learning curve.
Jordan
