1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
|
## std.options: Optional types.
## This module is imported by default.
use std.format
## The `Option` type.
## A type that represents either the presence or absence of a value.
pub type Option[T] = union
Some(T)
None
## Syntactic sugar for optional type declarations.
pub macro ?(T: type) =
quote Option[`T`]
## Directly accesses the inner value. Throws an exception if None.
pub func : T =
if self of Some(x) then x
else raise "empty"
## Indirect access. Propagates `None`.
pub macro ?[T](self: Option[T]) =
quote
match `self`
of Some(x) then x
of None then return None
## Checks if a type is present within an `Option` type.
pub func is_some[T](self: T?): bool =
self of Some(_)
## Checks if a type is not present within an `Option` type.
pub func is_none[T](self: T?): bool =
self of None
## Converts an `Option[T]` to a `Result[T, E]` given a user-provided error.
pub func err[T, E](self: T?, error: E): Result[T, E] =
if self of Some(x) then
Okay(x)
else
Error(error)
## Applies a function to `T`, if it exists.
pub func map[T, U](self: T?, fn: T -> U): U? =
if self of Some(x) then
Some(fn(x))
else
None
## Converts `T` to a `None`, if `fn` returns false and it exists.
pub func filter[T](self: T?, fn: T -> bool): T? =
if self of Some(x) and fn(x) then
Some(x)
else
None
## Applies a function to T, if it exists. Equivalent to `self.map(fn).flatten`.
pub func flatmap[T, U](self: T?, fn: T -> U?): U? =
if self of Some(x) then
fn(x)
else
None
## Converts from Option[Option[T]] to Option[T].
pub func flatten[T](self: T??): T? =
if self of Some(Some(x)) then
Some(x)
else
None
## Returns the inner value or a default.
pub func get_or[T](self: T?, default: T): T =
if self of Some(x) then x
else default
## Overloads the `==` operation for use on Options.
pub func ==[T](a, b: T?): bool =
if (a, b) of (Some(x), Some(y)) then
x == y
else
false
## Overloads the `str()` function for use on Options.
pub func str[T: Display](self: T?): str =
if self of Some(x) then
"Some({})".fmt(x.str)
else
"None"
examples
let x = Some(42)
if x of Some(y) then
assert x! == y
# references:
# https://nim-lang.github.io/Nim/options.html
# https://doc.rust-lang.org/std/option/enum.Option.html
|
