multithreading & sqlite

[monkyyy]

On Tuesday, 27 January 2026 at 16:38:08 UTC, Lars Johansson wrote:
> I have created a program using multithreading and Sqlite3.
> This is a prestudy for map&reduce.
>
> I found some parts of the program very hard to digest 
> especially the 'as!' crap.
> Sqlite was not simple (for me) to set up and use. It took some 
> time to understand I must make a physical copy of the result 
> (the .idup).
> It was hard to make this work.
>
> I would appreciate, if anyone can comment on things I can do 
> better:
> (On your own, it not easy to know what can be done better)
>
> import std.parallelism;
> import std.stdio;
> import core.thread;
> import std.array;
> import d2sqlite3;
>
>     void main() {
>         writeln("starting");
>         auto myresults = getData("mydata.db");
>         auto pool = new TaskPool(2); // Create pool with only 2 
> worker threads
>         foreach (i,row; pool.parallel(myresults)) {
>             writeln(row);
>            auto ID = row[0];
>            auto Name = row[1];
>            auto Age= row[2];
>     		writeln("Starting task ",i,  " ",ID, " ",Name, " ", Age);
>     		Thread.sleep(1.seconds);  // Simulate work
>             writeln("finish task ",i);
>         }
>         pool.finish();
>     }
>     string[][] getData(string DB){
>         string[][] results;
>         writeln("getData starts");
>         auto db = Database(DB);
>         foreach (row; db.execute("SELECT * FROM users")) {
>                 writeln("ID: ", row[0].as!int);   //WTF is this 
> as! crap
>                 writeln("Name: ", row[1].as!string);
>                 writeln("Age: ", row[2].as!int);
>             results ~= [
>                     row[0].as!string.idup,  // .idup makes 
> immutable copy
>                     row[1].as!string.idup,  // why do i need 
> this?
>                     row[2].as!string.idup   // and why do I 
> have to convert to string?
>             ];}
>             writeln("getData done");
>         return results;
>     }

`!` is a template call, and is always a template call; c syntax 
doesnt allow you to pass a type to a function 1 char and the 
double argument list was considered the best way forward.

I dont know where as comes from, but dup is used when you get a 
once off copy to a slice, `string` is *just* a one line of code 
`alias string=immutable char[]` in object. This make it a 
reference type.

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I dont like the api's people make for deserialization, this looks 
like a bad one. Look for something that parses an entire "row" as 
a struct that way your passing bundles of types already.