AA default value?

[Jarrett Billingsley]

"Janice Caron" <caron800 at googlemail.com> wrote in message 
news:mailman.24.1201263099.5260.digitalmars-d at puremagic.com...

> Wouldn't
> it be nicer if, instead, it simply returned
>
> typeof(aa[key]).init
>
> if the key was not present in the array?

What's funny is that a while ago ((long) before 1.0), if you looked up a key 
in an AA and the key didn't exist, it'd be added with a value of 
typeof(aa[key]).init.  So

int[int] aa;
writefln(aa[5]);

would give "0" as the output.

This was to mirror the behavior of C++'s std::map but many people opposed 
it, so now we have what we have now..

The issue is that you can't cover all the bases with a single type.  Some 
people want the auto-insertion, some don't.  Some want it to disallow 
updates, i.e. allow a key-value pair to be inserted but never modified. 
Some want the opposite, where you have to explicitly use an insert method to 
insert the values, but once they're in, they can be modified as much as you 
like.

At least the nice thing about the AAs is that they're simple to build custom 
containers on top of them, so most/all of these things can be implemented as 
structs wrapping them.  The downside is that with the current set of 
operator overloads and features, you can never make a custom type that can 
replace the builtin one in all cases.