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
