Associative array literal: length wrong when duplicate keys found

[John Colvin via Digitalmars-d-learn]

On Tuesday, 31 January 2017 at 14:15:58 UTC, Ivan Kazmenko wrote:
> Hi.
>
> I wanted to check whether a few variables of the same type are 
> all distinct, in a quick and dirty way.  I tried to do it 
> similar to Python's "len(set(value_list)) == len(value_list)" 
> idiom by using an associative array (AA).  At this point, I 
> found out that when initializing the AA with a literal, the 
> length is the number of keys given, regardless of whether some 
> of them were the same.
>
> A minimized example:
>
> -----
> import std.stdio;
> void main () {
> 	auto aa = [1 : 2, 1 : 3];
> 	writeln (aa.length, " ", aa); // 2 [1:3, ]
> }
> -----
>
> See, the length is 2, but iteration over aa yields only one 
> key:value pair.  Also, note the comma which is a sign of 
> internal confusion as well.
>
> My question is, what's the state of this?  Is this a bug?  Or 
> should it be forbidden to have such an initializer?  Or maybe 
> it is a feature with some actual merit?
>
> Ivan Kazmenko.

It's a bug, please report it. The initializer should be 
statically disallowed.

Adding a .dup works around the problem.

By the way, you can do sets like this, avoiding storing any dummy 
values, only keys:

struct Set(T)
{
	void[0][T] data;
	
	void insert(T x)
	{
		data[x] = (void[0]).init;
	}
	
	void remove(T x)
	{
		data.remove(x);
	}
	
	bool opBinaryRight(string op : "in")(T e)
	{
		return !!(e in data);
	}
	
	// other things like length, etc.
}

unittest
{
	Set!int s;
	s.insert(4);
	assert(4 in s);
	s.remove(4);
	assert(4 !in s);
}