##NaN on map keys, what to expect?

Question

Hi,

Doing some tests and arrived at the following scenario:

(assoc {##NaN nil} ##NaN nil)
=> {##NaN nil, ##NaN nil}

but trying to create a map like this is not possible:

{##NaN nil, ##NaN 1}

Could this be a bug in assoc? or is this the expected behavior

Answer 1

##NaN is not equal to anything else (including ##NaN), so you can't use it as a key in a map (probes to find it will never find it leading to strange behavior).