a := .1; b := .2
fmt.Println(a+b) returns 0.30000000000000004
fmt.Println(.1+.2) returns 0.3
Even worse, this persists into comparisons:
c := .3
a+b == c returns false
.1+.2 == c returns true
It's not a particularly big issue, mostly, but I'm sure it's confused someone before now, and will do so again.
Demo code: http://play.golang.org/p/FOv0JQRQJN
In most other cases the correct way is to check if the absolute value of the difference between one value and another is smaller than some arbitrary cut-off, a small number typically denoted with 'epsilon'.
The real problem is: most people don't have deep knowledge of how those details are implemented and take 'equality' for granted, especially if the visual representation of the numbers they are comparing tells them they should be equal which is not always the case.
The old adage goes: if you need floating point you don't understand your problem :)
The comment that sparked this sub-thread is a nice illustration of what can and does go wrong.