var x : u8 = 5; allows making type optional while keeping the code about the same, e.g. var x = 5; This arrangement has this nice consistency to it, with

var x : u8 = 5; allows making type optional while keeping the code about the same, e.g. var x = 5; This arrangement has this nice consistency to it, with the type info being more of a hint (to the compiler or to the programmer) than a required component.