Casting to a type held in a variable

I am attempting to cast a variable to a different type that is held in a variable or is the return type of a function. Here is the idea:

let i = 1 as type(of: 3.14)

But when I do this, I get a couple of errors:

• Use of undeclared type 'type'
• Consecutive statements on a line must be separated by ';' (This inserts a semi-colon between type and (of: 3.14))

And a warning:

• Expression of type (of: Double) is unused

How to I cast a value to a type that is held in a variable?