Result type that can hold either a value or an error, but not both
Add the following to your .nimble file:
requires "results"
or just drop the file in your project!
import results
# Re-export `results` so that API is always available to users of your module!
export results
# It's convenient to create an alias - most likely, you'll do just fine
# with strings or cstrings as error for a start
type R = Result[int, string]
# Once you have a type, use `ok` and `err`:
func works(): R =
# ok says it went... ok!
R.ok 42
func fails(): R =
# or type it like this, to not repeat the type:
result.err "bad luck"
func alsoWorks(): R =
# or just use the shortcut - auto-deduced from the return type!
ok(24)
if (let w = works(); w.isOk):
echo w[], " or use value: ", w.value
# In case you think your callers want to differentiate between errors:
type
Error = enum
a, b, c
type RE[T] = Result[T, Error]
# You can use the question mark operator to pass errors up the call stack
func f(): R =
let x = ?works() - ?fails()
assert false, "will never reach"
# If you provide this exception converter, this exception will be raised on
# `tryGet`:
func toException(v: Error): ref CatchableError = (ref CatchableError)(msg: $v)
try:
RE[int].err(a).tryGet()
except CatchableError:
echo "in here!"
# You can use `Opt[T]` as a replacement for `Option` = `Opt` is an alias for
# `Result[T, void]`, meaning you can use the full `Result` API on it:
let x = Opt[int].ok(42)
echo x.get()
# ... or `Result[void, E]` as a replacement for `bool`, providing extra error
# information!
let y = Result[void, string].err("computation failed")
echo y.error()
See results.nim for more in-depth documentation - specially towards the end where there are plenty of examples!
MIT license, just like Nim, or Apache, if you prefer that