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Update v4 spec about sharing props type #701

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Oct 27, 2022
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Update v4 spec about sharing props type #701

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02a3af8
update v4 spec about sharing props
mununki Oct 26, 2022
c052cb9
fix the example of shared props for v4 spec
mununki Oct 27, 2022
1112ae6
clean up the spec about shared props
mununki Oct 27, 2022
168d691
Update JSXV4.md
cristianoc Oct 27, 2022
4ef6c4b
update jsx v4 spec about shared props constraint
mununki Oct 27, 2022
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33 changes: 33 additions & 0 deletions cli/JSXV4.md
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Expand Up @@ -373,3 +373,36 @@ let p: A.props<_> = {x: "x", y: "y"}
<A x="X" {...p}>
<A {...p} {...p1}>
```

### Shared props type (new feature)

V4 introduces support to set a props type from the outside. It allows sharing of the props type between components.

```rescript
type sharedProps<'a> = {x: 'a, y: string}

module A = {
@react.component(:sharedProps<'a>)
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Would you clarify in the text above what's the role of <'a>. Does the name 'a matter, or is it only used to specify the number of type arguments?

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@mununki mununki Oct 26, 2022 •
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It is just telling the number of type arguments are available. Better to remove it?

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Not sure I understand: or can be 1 zero type args, or 2 more than zero. And the user needs to specify which one is true?

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@mununki mununki Oct 27, 2022 •
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Sorry for making communication cost. My point was that I expected there were some use cases:

type sp1 = ...

@react.component(:sp1)
type sp2<'a> = ...

@react.component(:sp2<'a>)
// or
@react.component(:sp2<string>)
type sp3<'a, 'b, ...> = ...

@react.component(:sp3<'a, 'b, ...>)
// or
@react.component(:sp3<string, 'b, ...>)

The text is saying that the type argument(s) is available. The name of 'a nor the number of type arguments wouldn't matter.

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Does it work also if the type definition has zero type arguments?

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If you mean this case:

type sp1 = ...

@react.component(:sp1)

Yes, it works. https://github.com/rescript-lang/syntax/blob/master/tests/ppx/react/expected/sharedProps.res.txt#L38

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@cristianoc cristianoc Oct 27, 2022 •
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I read the source code. So the number of type variables does matter. The name matters only so much as it normally matters, but not less.

So I think what's missing in the doc is one example with 0 and one with 2 type variables.

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@cristianoc cristianoc Oct 27, 2022 •
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One should also remark on the fact that a type called props cannot be defined in the current module or there will be a type error due to type redefinition. (It could at most be defined outside the current module)

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One should also remark on the fact that a type called props cannot be defined in the current module or there will be a type error due to type redefinition. (It could at most be defined outside the current module)

I think this is already noted as https://github.com/rescript-lang/syntax/blob/master/cli/JSXV4.md#transformation-for-component-definition

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@mununki mununki Oct 27, 2022 •
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How does it look? c052cb9 1112ae6

let make = (~x, ~y) => React.string(x ++ y)
}

module B = {
@react.component(:sharedProps<'a>)
let make = (~x, ~y) => React.string(x ++ y)
}

// is transformed to
module A = {
type props<'a> = sharedProps<'a>

let make = ({x, y, _}: props<'a>) => React.string(x ++ y)
...
}

module B = {
type props<'a> = sharedProps<'a>

let make = ({x, y, _}: props<'a>) => React.string(x ++ y)
...
}
```