Struct hash issues with string fields

[Jonathan M Davis]

On Saturday, May 26, 2012 21:53:07 Andrej Mitrovic wrote:
> I don't understand this:
> 
> import std.stdio;
> 
> struct Symbol { string val; }
> 
> void main()
> {
>     int[string] hash1;
>     hash1["1".idup] = 1;
>     hash1["1".idup] = 2;
>     writeln(hash1);  // writes "["1":2]"
> 
>     int[Symbol] hash2;
>     Symbol sym1 = Symbol("1".idup);
>     Symbol sym2 = Symbol("1".idup);
>     hash2[sym1] = 1;
>     hash2[sym2] = 1;
>     writeln(hash2);  // writes "[Symbol("1"):1, Symbol("1"):1]"
> }
> 
> Why are sym1 and sym2 unique keys in hash2? Because the hash
> implementation checks the array pointer instead of its contents? But
> then why does hash1 not have the same issue?
> 
> I can't override toHash() in a struct, so what am I supposed to do in
> order to make "sym1" and "sym2" be stored into the same hash key?

Why can't you have a toHash in your struct? Your struct should be able to have 
a toHash just like it can have a toString. If anything, I find it disturbing 
that the code compiles _without_ a definition for opHash in the struct.

Now, that aside, the results with hash2 definitely look like a bug to me. It's 
probably just the result of one more of the many issues with the current AA 
implementation.

- Jonathan M Davis