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Update parameter-freedom.md #14

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21 changes: 13 additions & 8 deletions in-progress/parameter-freedom.md
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Expand Up @@ -756,21 +756,23 @@ when taking into account optional and rest parameters.

5. **Handle rest and spread parameters.** If there is a rest parameter:

1. Let `restCount` be the `argCount -required.length - optional.length`.
1. Let `restCount` be the `argCount - required.length - optional.length`.
This is the number of extra arguments that will get bound to the rest
parameter. It may be negative.

2. If `restCount` is non-negative, then:

1. Let `restParam` be the index of the rest parameter in the list of
positional parameters, if there is one.
positional parameters.

2. Extract the rest arguments from `restParam` to `restParam +
restCount` and replace them with the result. (See below.)

Else (no rest arguments):

1. Bind the rest parameter to `const List<Null>[]`.
1. Bind the rest parameter to an unmodifable empty instance of `List<T>`
where `T` is the type specified in the declaration of the rest parameter,
if any.

Else (no rest parameter):

Expand Down Expand Up @@ -889,9 +891,12 @@ proposal. To determine if function type `Type` is a subtype of function type
2. For each parameter position in `Supe`:

1. Let `pSupe` be the parameter at that position in `Supe`. Let `pType` be
the parameter at that position in `Type`.
the parameter at that position in `Type`, if any.

1. If there is no such parameter in Type, `Type` is not a subtype.

1. If `pSupe` is not a subtype of `pType`, `Type` is not a subtype.
1. If the type of `pSupe` is not a subtype of the type of `pType`,
`Type` is not a subtype.
This is the usual contravariant parameter rule.

3. If `pSupe` is rest and `pType` is not, or vice versa, `Type` is
Expand All @@ -910,8 +915,8 @@ proposal. To determine if function type `Type` is a subtype of function type
*The effective restriction is that required parameters in the
supertype must usually stay required in the subtype. However, a
subtype can make one or more required parameters optional if all
optional parameters in the supertype are after all of its required
parameters. It's OK for a rest parameter to be anywhere in there.
of them occur immediately before the first optional parameter
of the supertype. It's OK for a rest parameter to be anywhere in there.
This follows the existing Dart rules.*

3. If `Supe` has a rest parameter and `Type` has more positional parameters
Expand All @@ -921,7 +926,7 @@ proposal. To determine if function type `Type` is a subtype of function type
the rest parameter.

3. For each parameter position in `Type` beyond the last parameter position in
`Supe` (i.e. for the extra parameters `Supe` has at the end):
`Supe` (i.e. for the extra parameters `Type` has at the end):

1. If the parameter is required, `Type` is not a subtype. You can only add
optional parameters and/or a rest parameter.
Expand Down