Array Concatenate

[Jonathan M Davis]

On Friday, June 08, 2012 14:41:10 Paul wrote:
> If this works...
> 
> D programming book section 4.1.9 Expanding
> auto a = [87, 40, 10];
> a ~= 42;
> assert(a== [87, 40, 10, 42]);

That compiles just fine.

> why doesnt' this work?
> 
> DeletedBlks ~= matchOld[0];
> 
> the dmd compiler comes back with
> Error: cannot append type string to type string[ulong]
> 
> Does this append operator only work for literals?

You didn't give us the types of either DeletedBlks or matchOld[0]. However, 
from the error, it looks like DeletedBlks is a string[ulong], and matchOld[0] 
is a string. string[ulong] is an associate array - which means that it's a 
hash table - and appending doesn't make any sense with an associative array, 
because AAs aren't ordered. They take key-value pairs. So, something like

DeletedBlks[42] = matchOld[0];

should compile - which creates the key-value pair of 42 and the value of 
matchOld[0].

Section 4.4 of TDPL discusses associative arrays (which you obviously aren't 
far from, since you're referring to section 4.1.9). So, read that section, and 
things should be clearer.

- Jonathan M Davis