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Diffstat (limited to 'docs/optionals.md')
| -rw-r--r-- | docs/optionals.md | 30 |
1 files changed, 8 insertions, 22 deletions
diff --git a/docs/optionals.md b/docs/optionals.md index bfebd94e..131daf19 100644 --- a/docs/optionals.md +++ b/docs/optionals.md @@ -47,24 +47,23 @@ Similarly, if you wanted to declare a variable that could be a list of texts or none and initialize it as none, you would write: ```tomo -x := ![Text] +x : [Text]? = none ``` If you want to declare a variable and initialize it with a non-none value, but -keep open the possibility of assigning `none` later, you can use the postfix -`?` operator to indicate that a value is optional: +keep open the possibility of assigning `none` later, you can declare the type +to be optional, but assign a non-none value: ```tomo -x := 5? +x : Int? = 5 # Later on, assign none: x = none ``` ## Type Inference -For convenience, `none` can also be written without the explicit type -annotation for any type in situations where the compiler knows what type of -optional value is expected: +For convenience, `none` is an optional value whose type is inferred from the +context where it's used. Some examples are: - When assigning to a variable that has already been declared as optional. - When returning from a function with an explicit optional return type. @@ -73,7 +72,7 @@ optional value is expected: Here are some examples: ```tomo -x := 5? +x : Int? x = none func doop(arg:Int? -> Text?) @@ -82,19 +81,6 @@ func doop(arg:Int? -> Text?) doop(none) ``` -Non-none values can also be automatically promoted to optional values without -the need for an explicit `?` operator in the cases listed above: - -```tomo -x : Int? = none -x = 5 - -func doop(arg:Int? -> Text?) - return "okay" - -doop(123) -``` - ## None Checking In addition to using conditionals to check for `none`, you can also use `or` to @@ -103,7 +89,7 @@ providing an early out statement like `return`/`skip`/`stop` or a function with an `Abort` type like `fail()` or `exit()`: ```tomo -maybe_x := 5? +maybe_x : Int? = 5 >> maybe_x or -1 = 5 : Int >> maybe_x or fail("No value!") |