User Defined Range Type : to replace clamp functions : let the type system help us.
Instead of using a clamp or an if 1<x and x<9 {}.
Let us define a new range type
-
use as parameter type or return type, also for assignment.
-
type oneToNine = (1…9, 2);
-
type oneToNine for (1…9, 2);
-
inclusive syntax : (1…9, 2) is also allowed.
-
oneToNine is a user-defined range type
-
from the range constructor or syntax builder.
-
value range : from 1 to 9 exclusive, in step 2
- possible valid values : 1, 3, 5, 7 only
- any other values would cause an error : type boundary violation or invalid value.
- Is this a compile time type-check?
- let the type system do the work, YES.
- No More Clamp Fn, YES.
-
fn getme6(val: oneToNine) -> i32; // error, no 6 in range.
-
fn getme7(val: oneToNine) -> i32; // yes i am in range.
-
How to express i32, i64, i16, u32, etc of range values.
-
what is the range value type?
-
New syntax : type oneToNine = (1…9, 2) for u64;
Alternative :
- New syntax : type oneToNine = (1…9, 2) with u64;
- New syntax : type oneToNine = (1…9, 2) of u32;
- New syntax : type oneToNine = (1…9, 2) where u128;
REAL WORLD USAGE : github.com/netvl/xml-rs/src/common.rs
// a range type is more effective instead of u8 to u64
// count: u64 is the final item, why not as param.
// to prevent a large number from being passed into the fn.
pub fn advance(&mut self, count: u8) {
self.column = self.column + count as u64;
}
// here again, a shortcut to u64.
pub fn advance_to_tab(&mut self, width: u8) -> () { let width = width as u64;
self.column = self.column + width - self.column % width
}