Welcome to the community Monty!
They are not the exact same.
var temp:MyStructure = MyStructure()
This creates a variable called temp, and initializes it to a new instance of MyStructure
This creates a variable temp1, of type MyStructure but it is not set to a value, so if you print it, it’ll be nil
The first one can be shortened because of type inference, the compiler knows it’s type MyStructure because you’re giving it a value at initialization.
var temp = MyStructure()
Overall I’d say you’ll use the first one more often than the second. (Relatively) Rarely do you declare a variable, but not give it a value