Julia's type system is unique. Julia behaves as a dynamically typed language (such as Python, for instance) most of the time. This means that a variable bound to an integer at one point might later be bound to a string. For example, consider the following:
julia> x = 10 10 julia> x = "hello" "hello"
However, one can, optionally, add type information to a variable. This causes the variable to only accept values that match that specific type. This is done through a type of annotation. For instance, declaring x::String implies that only strings can be bound to x; in general, it looks like var::TypeName. These are used the most often to qualify the arguments a function can take. The extra type information is useful for documenting the code, and often allows the JIT compiler to generate better-optimized native code. It also allows the development...