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Date: Fri, 8 Sep 2023 23:27:10 +0300
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Subject: Re: [PHP-DEV] RFC Proposal: Readonly Structs in PHP
From: someniatko@gmail.com (someniatko)

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Hi internals!

I think it can be useful for structured data obtained from decoding JSONs
or from a relational database. However, maybe there is an even better idea,
which combines the best of two worlds: the world of your structs RFC, and
native PHP arrays - something like "array shapes".

For instance, taking the syntax from your proposed RFC (but perhaps the
keyword changed to `shape`, or perhaps `array class` to reuse keywords -
let's not bikeshed here) to define a shape, and adding a function like
`array_shape_coerce($array, $shapeType)` which internally marks an array to
be of a defined shape if it matches its definition (throws an exception
otherwise, or perhaps returns true/false value or an enum for
success/failure) and allows it to be passed where a certain shape type is
expected. I think this could be a better approach than pure structs because
it leaves all array-based PHP machinery available to such "structs", like
`array_map()`, `array_filter()` etc.

There is an open question of whether array coerced to shapes can be
modified, and if yes, how to react to modifications. Perhaps the easiest
solution is to have another function along the lines
`array_shape_seal($array, $shapeType)` which not only marks array to be of
shape (if the given array matches given shape), but also permits only such
modifications which keep the array to be of this shape. And if the regular
`array_shape_coerce` is used, then any modifications are permitted, but the
array "loses" its shape.

Regards,
Illia / someniatko

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