Type instability if I map over array of functions

General Usage
2

Function is an abstract type. Look at

julia> typeof(init_add(StructA(1.1)))
##3#4{StructA}

julia> typeof(init_add(StructB(2.2)))
##5#6{StructB}

Since these types are different, iterating over a Vector containing elements of both types is the same as iterating over any other type-heterogeneous collection (e.g. Number[1, 2.0]). See this post for example for some options.