[Proposal] Struct Data Types

On Fri, Mar 15, 2019 at 4:49 AM Kenneth Ellis McCall xellisx@gmail.com
wrote:

Hey all,

I'm looking to get feedback on a RFC I want to propose.

PHP RFC: Addition of the 'struct' data type.

Introduction:
PHP has many data types, but does not offer something that is the
equivalent to the C struct data type.

The purpose of this RFC is to propose a data type of 'struct', which
would be a strictly typed, immutable data structure that resembles a mix
of a class and an array.

Pros:
Provides a data type which would immutable and self-validating by
mandatory type hinting.

Cons:
?

Possible future considerations:
Advanced Type Validators.

Use cases:
Configurations, DTOs, anything that needs a strict schema.

Proposed usage / syntax:
struct MyStuct
{
boolean|bool 'prop01';
integer|int 'prop02';
double 'prop03';
string 'prop04';
array 'prop05';
object 'prop06';
resource 'prop07';
callable 'prop08';
iterable 'prop09';
Acme\MyClass 'prop10';
Acme\ConfStruct 'prop11';
array Acme\AnotherStruct 'prop12';
?boolean|bool 'prop13';
?integer|int 'prop14';
?double 'prop15';
?string 'prop16';
?array 'prop17';
?object 'prop18';
?resource 'prop19';
?callable 'prop20';
?iterable 'prop21';
?Acme\MyClass 'prop22';
?Acme\ConfStruct 'prop23';
?array Acme\AnotherStruct 'prop24';
}
OR?

struct MyStuct
{
'prop01': boolean|bool;
'prop02': integer|int;
'prop03': float;
'prop04': string;
'prop05': array;
'prop06': object;
'prop07': resource;
'prop08': callable;
'prop09': iterable;
'prop10': Acme\MyClass;
'prop11': Acme\ConfStruct;
'prop12': array Acme\AnotherStruct;
'prop13': ?boolean|bool;
'prop14': ?integer|int;
'prop15': ?float;
'prop16': ?string;
'prop17': ?array;
'prop18': ?object;
'prop19': ?resource;
'prop20': ?callable;
'prop21': ?iterable;
'prop22': ?Acme\MyClass;
'prop23': ?Acme\ConfStruct;
'prop24': ?array Acme\AnotherStruct;
}

struct Acme\ConfStruct
{
string 'host';
?int 'port';
}

struct Acme\AnotherStruct
{
string 'firstName';
string 'lastName';
?integer 'age';
}

Acme\ConfStruct $a = {
'host' => '127.0.0.1',
'port' => 8088
}

Acme\MyStruct $myStruct = {
'prop01' => true,
'prop02' => 1,
'prop03' => 1.01,
'prop04' => 'Hello',
'prop05' => ['a', 'b', 'c'],
'prop06' => new stdClass(),
'prop07' => fopen('xyz.txt', 'wb'),
'prop08' => function() {
return 1 + 1;
},
'prop09' => [
[1, 2, 3],
[4, 5, 6],
[7, 8, 9]
],
'prop10' => new Acme\MyClass,
'prop11' => $a,
'prop12' => [
Acme\AnotherStruct [
'firstName' => 'Bob',
'lastName' => 'Walker'
],
Acme\AnotherStruct [
'firstName' => 'Little',
'lastName' => 'Johnny',
'age' => 5
],
],
'prop13' => null,
'prop14' => null,
'prop15' => null,
'prop16' => null,
'prop17' => null,
'prop18' => null,
'prop19' => null,
'prop20' => null,
'prop21' => null,
'prop22' => null,
'prop23' => null,
'prop24' => null
};

$x = new Some\Other\Class($myStruct);

echo $myStruct['prop02'];
OR?

echo $myStruct->prop02;
Warning / Errors / Exceptions:
Acme\MyStruct $a = {
'prop01' => 5,
...
}
// Should: throw new TypeError("'prop01' should be set as a boolean
type, integer type was attempted.")

echo $a['xyz']; // or echo $a->xyz (which ever is the preferred syntax
after comments).
// Should: trigger_error("<b>Notice</b>: Undefined property:
Acme\MyStruct::xyz");

https://github.com/ellisgl/PHP-RFC-Struct-Data-Type

I think this a worthwhile topic to pursue -- immutable value objects are
certainly seeing increased use, and it would be great to increase support
for them. What I mainly wonder in regard to this RFC is: Do we really need
a new struct type with a new syntax, or can we get this as a combination of
multiple features for existing class types? In particular, I think your
struct type proposal can be split into these three parts:

1. Property types. As of PHP 7.4 these are already available, yay! Your
   example also make use of some types (e.g. union types) that are not
   currently supported, but likely will be in the future.

2. Readonly properties: Without requiring an entire object to be immutable,
   we can add support for readonly properties. This may be either a standalone
   feature, or part of / based on a more general property accessors proposal.

3. Object construction syntax: The last part is a syntax to construct
   objects without a constructor, using a syntax where property names are
   specified, and which ensures that all non-default properties are
   initialized.

Your example

// declaration
struct AnotherStruct
{
string 'firstName';
string 'lastName';
?int 'age';
}
// initialization
AnotherStruct [
'firstName' => 'Little',
'lastName' => 'Johnny',
'age' => 5
]

could then become something like

// declaration
class AnotherStruct {
readonly string $firstName;
readonly string $lastName;
readonly ?int $age = null;
}
// initialization (syntax up to bikeshedding)
new AnotherStruct {
$firstName => 'Little',
$lastName => 'Johnny',
$age => 5,
}

I'd generally prefer a solution that is based on the existing class system.
Especially as it means that other use-cases can also benefit: Sometimes you
might only want some of your properties to be readonly, etc.

Nikita

could then become something like

// declaration
class AnotherStruct {
readonly string $firstName;
readonly string $lastName;
readonly ?int $age = null;
}
// initialization (syntax up to bikeshedding)
new AnotherStruct {
$firstName => 'Little',
$lastName => 'Johnny',
$age => 5,
}

I'd generally prefer a solution that is based on the existing class system.
Especially as it means that other use-cases can also benefit: Sometimes you
might only want some of your properties to be readonly, etc.

There is also more room to add formal validation so we could have
class AnotherStruct {
readonly string(64) $firstName;
readonly string(64) $lastName;
readonly ?int(0-150) $age = null;
}

Although I would perhaps expect in this case to have 'date of birth' as
'immutable' while age is something that will be variable.
But isn't all this just mainly another class object. As has been
suggested for an improved array object but never developed further?
Create an extension to support it first, although the validation element
is still needed for any variable across the board ...

--
Lester Caine - G8HFL

Contact - https://lsces.co.uk/wiki/?page=contact
L.S.Caine Electronic Services - https://lsces.co.uk
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Rainbow Digital Media - https://rainbowdigitalmedia.co.uk

On Fri, Mar 15, 2019 at 4:49 AM Kenneth Ellis McCall xellisx@gmail.com
wrote:

Hey all,

I'm looking to get feedback on a RFC I want to propose.

PHP RFC: Addition of the 'struct' data type.

Introduction:
PHP has many data types, but does not offer something that is the
equivalent to the C struct data type.

The purpose of this RFC is to propose a data type of 'struct', which
would be a strictly typed, immutable data structure that resembles a mix
of a class and an array.

Pros:
Provides a data type which would immutable and self-validating by
mandatory type hinting.

Cons:
?

Possible future considerations:
Advanced Type Validators.

Use cases:
Configurations, DTOs, anything that needs a strict schema.

Proposed usage / syntax:
struct MyStuct
{
boolean|bool 'prop01';
integer|int 'prop02';
double 'prop03';
string 'prop04';
array 'prop05';
object 'prop06';
resource 'prop07';
callable 'prop08';
iterable 'prop09';
Acme\MyClass 'prop10';
Acme\ConfStruct 'prop11';
array Acme\AnotherStruct 'prop12';
?boolean|bool 'prop13';
?integer|int 'prop14';
?double 'prop15';
?string 'prop16';
?array 'prop17';
?object 'prop18';
?resource 'prop19';
?callable 'prop20';
?iterable 'prop21';
?Acme\MyClass 'prop22';
?Acme\ConfStruct 'prop23';
?array Acme\AnotherStruct 'prop24';
}
OR?

struct MyStuct
{
'prop01': boolean|bool;
'prop02': integer|int;
'prop03': float;
'prop04': string;
'prop05': array;
'prop06': object;
'prop07': resource;
'prop08': callable;
'prop09': iterable;
'prop10': Acme\MyClass;
'prop11': Acme\ConfStruct;
'prop12': array Acme\AnotherStruct;
'prop13': ?boolean|bool;
'prop14': ?integer|int;
'prop15': ?float;
'prop16': ?string;
'prop17': ?array;
'prop18': ?object;
'prop19': ?resource;
'prop20': ?callable;
'prop21': ?iterable;
'prop22': ?Acme\MyClass;
'prop23': ?Acme\ConfStruct;
'prop24': ?array Acme\AnotherStruct;
}

struct Acme\ConfStruct
{
string 'host';
?int 'port';
}

struct Acme\AnotherStruct
{
string 'firstName';
string 'lastName';
?integer 'age';
}

Acme\ConfStruct $a = {
'host' => '127.0.0.1',
'port' => 8088
}

Acme\MyStruct $myStruct = {
'prop01' => true,
'prop02' => 1,
'prop03' => 1.01,
'prop04' => 'Hello',
'prop05' => ['a', 'b', 'c'],
'prop06' => new stdClass(),
'prop07' => fopen('xyz.txt', 'wb'),
'prop08' => function() {
return 1 + 1;
},
'prop09' => [
[1, 2, 3],
[4, 5, 6],
[7, 8, 9]
],
'prop10' => new Acme\MyClass,
'prop11' => $a,
'prop12' => [
Acme\AnotherStruct [
'firstName' => 'Bob',
'lastName' => 'Walker'
],
Acme\AnotherStruct [
'firstName' => 'Little',
'lastName' => 'Johnny',
'age' => 5
],
],
'prop13' => null,
'prop14' => null,
'prop15' => null,
'prop16' => null,
'prop17' => null,
'prop18' => null,
'prop19' => null,
'prop20' => null,
'prop21' => null,
'prop22' => null,
'prop23' => null,
'prop24' => null
};

$x = new Some\Other\Class($myStruct);

echo $myStruct['prop02'];
OR?

echo $myStruct->prop02;
Warning / Errors / Exceptions:
Acme\MyStruct $a = {
'prop01' => 5,
...
}
// Should: throw new TypeError("'prop01' should be set as a boolean
type, integer type was attempted.")

echo $a['xyz']; // or echo $a->xyz (which ever is the preferred syntax
after comments).
// Should: trigger_error("<b>Notice</b>: Undefined property:
Acme\MyStruct::xyz");

https://github.com/ellisgl/PHP-RFC-Struct-Data-Type

I think this a worthwhile topic to pursue -- immutable value objects are
certainly seeing increased use, and it would be great to increase support
for them. What I mainly wonder in regard to this RFC is: Do we really need
a new struct type with a new syntax, or can we get this as a combination of
multiple features for existing class types? In particular, I think your
struct type proposal can be split into these three parts:

I guess needing a new datatype depends if the struct should be passed by
value instead of by reference.

1. Property types. As of PHP 7.4 these are already available, yay! Your
   example also make use of some types (e.g. union types) that are not
   currently supported, but likely will be in the future.

2. Readonly properties: Without requiring an entire object to be immutable,
   we can add support for readonly properties. This may be either a standalone
   feature, or part of / based on a more general property accessors proposal.

Read Only types would be a good idea, DOM already uses readonly as a pseudo
keyword to describe their custom property handlers.
A lot of internal classes could benefit from exposing this explicitly.

3. Object construction syntax: The last part is a syntax to construct
   objects without a constructor, using a syntax where property names are
   specified, and which ensures that all non-default properties are
   initialized.

Your example

// declaration
struct AnotherStruct
{
string 'firstName';
string 'lastName';
?int 'age';
}
// initialization
AnotherStruct [
'firstName' => 'Little',
'lastName' => 'Johnny',
'age' => 5
]

could then become something like

// declaration
class AnotherStruct {
readonly string $firstName;
readonly string $lastName;
readonly ?int $age = null;
}
// initialization (syntax up to bikeshedding)
new AnotherStruct {
$firstName => 'Little',
$lastName => 'Johnny',
$age => 5,
}

I'd generally prefer a solution that is based on the existing class system.
Especially as it means that other use-cases can also benefit: Sometimes you
might only want some of your properties to be readonly, etc.

Nikita

2. Readonly properties: Without requiring an entire object to be immutable,
   we can add support for readonly properties. This may be either a standalone
   feature, or part of / based on a more general property accessors proposal.

This is reasonable, but only if true immutability is the aim, rather than
pass-by-value / copy-on-write.

True immutability is probably fine for small structs, like Point(x, y) or
Money(currency, value), because any "modification" can just construct a new
instance manually. But in some cases, it's more convenient to have the
copying implicit, rather than needing a whole set of withFoo methods.

Note that you could have COW structs with optional immutability, and get
the best of both worlds:

struct Foo {
readonly int $one;
int $two;
}
$foo = new Foo(1,2);
$bar = $foo; // implicit copy-on-write clone
$bar->two = 3; // sets the property on $bar, leaving $foo untouched
$bar->one = 42; // error

I'm not sure how to do this with only reference types plus readonly
properties; you'd need some kind of "partial clone":

class Foo {
readonly int $one;
readonly int $two;
}
$foo = new Foo(1,2);
$bar = clone $foo { two => 3 }; // need to set the new property value while
constructing, because it's readonly
$bar->two = 3; // error
$bar->one = 42; // error

Regards,

Rowan Collins
[IMSoP]