That type parameter syntax is really off, you can't have default values for
generics and you don't define static types like `static[U]: int`. I also don't
think `const T` is a valid return type
Static types essentially accept compile time constants and can be used in
routine call/type parameters. I'll show code to explain because it's fairly
simple.
proc foo1[T: static[int]](value: bool): array[T, bool] =
for i in 0..<T:
result[i] = value
let arr1 = foo1[3](true)
doAssert(arr1[2] == true)
proc foo2(length: static[int], value: bool): array[length, bool] =
for i in 0..<length:
result[i] = value
let arr1 = foo1(3, false)
doAssert(arr1[2] == false)
type A = static[int] # this works too, and you can replace static[int]
usages with it
Run
Typedesc is similar in that instead of being a compile time constant it's a
compile time type, and is a way of moving type parameters into the call
parameter list.
proc foo1[T](param: int) = discard
proc foo2(T: typedesc, param: int) = discard
foo1[Exception](5)
foo2(Exception, 5)
proc foo3[T: Exception](param: int) = discard
proc foo4(T: typedesc[Exception], param: int) = discard
foo3[IOError](5)
foo4(IOError, 5)
Run
Recent versions of Nim have `T: type Exception` as sugar for `T:
typedesc[Exception]` so don't be confused if you see that too.
