Add discussion of 'some' on parameter types [SE-0341] #350
Conversation
- Start with the generic syntax, since that's what readers have seen in previous chapters already. - Walk through an example of using 'some' more than once. - Match func/subscript/init order in prose to chapter ordering.
| ``` | ||
|
|
||
| The `drawTwiceGeneric(_:)` function | ||
| uses a generic type parameter named `SomeShape`, |
|
|
||
| The `drawTwiceGeneric(_:)` function | ||
| uses a generic type parameter named `SomeShape`, | ||
| and explicitly includes the protocol conformance requirement. |
There was a problem hiding this comment.
s/includes/states/ ?
Also do we call them "requirements" or "constraints" here? You also use "constraint" below
There was a problem hiding this comment.
Reworded & changed. The chapter on generics also calls these "constraints".
| in this case, one triangle and one trapezoid. | ||
| If you need to write a function | ||
| that has multiple generic parameters | ||
| and constrain them to be are all the same type, |
| If you need to write a function | ||
| that has multiple generic parameters | ||
| and constrain them to be are all the same type, | ||
| use the usual generic syntax instead. |
There was a problem hiding this comment.
Clarify "usual syntax": s/usual generic syntax/syntax for a named generic type parameter/ ?
There was a problem hiding this comment.
Changed. Good point that both of these syntaxes can be considered "usual" now & in the future.
TSPL.docc/LanguageGuide/Generics.md
Outdated
| to indicate that they're a placeholder for a *type*, not a value. | ||
|
|
||
| > Note: | ||
| > If you don't need to name a type parameter or give it any constraints, |
There was a problem hiding this comment.
More precisely, opaque parameters can be subject to conformance and superclass requirements -- that's the part that follows the some keyword. But they can't be subject to same-type requirements
| ## Opaque Parameter Types | ||
|
|
||
| In addition to writing `some` to return an opaque type, | ||
| you can also write `some` in the type for a parameter |
There was a problem hiding this comment.
Maybe that's a bigger change than what you're after here, but I would introduce some parameters first, before some returns maybe.
There was a problem hiding this comment.
We can revisit, but I think I'd like to keep this structure. The some syntax serves two purposes: as a lightweight syntax for generics — generics have their own discussion elsewhere — and as opaque return types. So the new concept that some brings is opaque types.
Co-authored-by: Slava Pestov <[email protected]>
Edits from <rdar://145499286>.
Fixes: rdar://143326925