I just hunted quite some time for a bug that was because I'm using structs
as the key for associative arrays.
It worked without problem for a long time, and now after I added a string to
the struct the associative array wouldnt work.

I found in the documentation:
" If the KeyType is a struct type, a default mechanism is used to compute
the hash and comparisons of it based on the binary data within the struct
value. A custom mechanism can be used by providing the following functions
as struct members:"
uint toHash();
int opCmp(KeyType* s);

After I implemented these everything worked fine.

I wrote a simple test to check if it was because of the string, but everything worked in my testcase. So I'm wondering what actually broke it...

"Simen Haugen" <simen@norstat.no> wrote in message news:f0if23$24mj$2@digitalmars.com...
>I just hunted quite some time for a bug that was because I'm using structs
> as the key for associative arrays.
> It worked without problem for a long time, and now after I added a string
> to
> the struct the associative array wouldnt work.
>
> I found in the documentation:
> " If the KeyType is a struct type, a default mechanism is used to compute
> the hash and comparisons of it based on the binary data within the struct
> value. A custom mechanism can be used by providing the following functions
> as struct members:"
> uint toHash();
> int opCmp(KeyType* s);
>
> After I implemented these everything worked fine.
>
> I wrote a simple test to check if it was because of the string, but everything worked in my testcase. So I'm wondering what actually broke it...

It's because strings are reference types.  Even if you had the same string value for both structs, they could be pointing to two different memory locations, so when the default struct hashing mechanism computes the hash, it doesn't take the string value into account, just the reference; hence, two structs with the same string value would hash to different locations.

"Simen Haugen" <simen@norstat.no> wrote in message news:f0if23$24mj$2@digitalmars.com...
>I just hunted quite some time for a bug that was because I'm using structs
> as the key for associative arrays.
> It worked without problem for a long time, and now after I added a string
> to
> the struct the associative array wouldnt work.
>
> I found in the documentation:
> " If the KeyType is a struct type, a default mechanism is used to compute
> the hash and comparisons of it based on the binary data within the struct
> value. A custom mechanism can be used by providing the following functions
> as struct members:"
> uint toHash();
> int opCmp(KeyType* s);
>
> After I implemented these everything worked fine.
>
> I wrote a simple test to check if it was because of the string, but everything worked in my testcase. So I'm wondering what actually broke it...

It's because strings are reference types.  Even if you had the same string value for both structs, they could be pointing to two different memory locations, so when the default struct hashing mechanism computes the hash, it doesn't take the string value into account, just the reference; hence, two structs with the same string value would hash to different locations.

"Jarrett Billingsley" <kb3ctd2@yahoo.com> wrote in message news:f0ifjl$25d0$1@digitalmars.com...

Oh, what the eff, newsgroup.