The type is inferred on all 4 lines and the mechanism is little different; the 4th line is the most complex one, because there's a type unification required acr

The type is inferred on all 4 lines and the mechanism is little different; the 4th line is the most complex one, because there's a type unification required across all elements of the array, but C# and Java and other languages with overloading already need to do very similar inference with the ternary operator - the types on each side of the branch need to be unified to resolve the overload. Hindley-Milner type inference (like used in F#) isn't hugely more complex; it's more aggressive at using type variables to generalize the code, and applies type unification in more situations.