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--- rfc:compact-object-property-assignment [2020/03/12 02:19] – jgivoni
+++ rfc:compact-object-property-assignment [2020/04/14 06:30] (current) – jgivoni
@@ Line 1: / Line 1: @@
 ====== PHP RFC: Compact Object Property Assignment ======
-  * Version: 0.9
-  * Date: 2020-03-10
+**COPA: A //pragmatic// approach to object literals**
+  * Version: 1.3
+  * Date: 2020-03-17
   * Author: Jakob Givoni <jakob@givoni.dk>
-  * Status: Draft
+  * Status: Declined
+  * Discussion: [[https://externals.io/message/109055]]
 ===== Introduction =====
 ==== Summary ====
-**A pragmatic approach to mimicking object literals.**
 This RFC proposes a new, compact syntax to assign values to multiple properties on an object in a single expression.
+This //**pseudo object literal**// notation, (though not limited to such use) is intended to enable the developer to //**create an object and populating it inline**//, f.ex. directly as an argument in a function call.
+As an alternative to writing a data structure as an associative array, COPA gives the data a **//documented signature//** so that you know what parameters are expected and their value types.
+> COPA does not introduce any new concepts or complexities, but merely a new syntax aimed at making millions of PHP developers write their code in a simpler way. The code becomes easier to write and read and thus more maintainable without any lateral limitations or factual downsides.
 ==== Example ====
+Let’s start with an example that demonstrates the essence of COPA.
 === Instead of doing this... ===
 <code php>
-$myObj->prop_a = 1;
+$myObj->a = 1;
-$myObj->prop_b = 2;
+$myObj->b = 2;
-$myObj->prop_c = 3;
+$myObj->c = 3;
 </code>
 === You will be able to do this: ===
 <code php>
 $myObj->[
-    prop_a = 1,
+    a = 1,
-    prop_b = 2,
+    b = 2,
-    prop_c = 3,
+    c = 3,
 ];
 </code>
+> COPA is everything that comes after the object expression. You can use COPA on any expression that evaluates to an object. COPA is not tied to object construction, but can be used anytime, anywhere in the objects life, as many times as you want.
+//See more use cases below.//
 ==== Motivation ====
-The purpose of this feature is to lighten the effort of populating data structures, especially medium to large ones.
-Ideally the solution should meets the following criteria:
+The purpose of this feature is to lighten the effort of creating, populating and sending data structures, from small to large ones.
+The goal was to find a solution that meets the following criteria:
   * **Brief** - only mention the object once (less repetition)
@@ Line 39: / Line 55: @@
   * **Typo-proof** - property names can be autocompleted easily by IDE (faster typing, fewer errors)
   * **Type-checking** - IDE can verify correct type for typed properties and annotated virtual properties
-  * **Order-agnostic** - properties can be specified in any order (this doesn't mean that the result is necessarily the same for any ordering, as that will depend on the object implementation)
+  * **Order-agnostic** - properties can be specified in any order (though note that the order //may// change the result!)
-  * **Sparcity** - there's no obligation to specify any particular property (non-specified properties may be given a default value)
+  * **Sparcity** - any property can be “skipped” (“skipped” properties may acquire a default value)
   * **Simple** - does what you would expect without introducing any new concepts into the language
+> My focus is to find a **pragmatic** solution that is trivial to implement, and won’t impede futher development of the language.
+//If you have ever wanted to create, populate and send an object inside a function call, COPA is for you!//
 ===== Proposal =====
 ==== Syntax ====
-The proposed syntax following an object expression ''%%$myObj%%'' | ''%%(new MyClass())%%'' is the object arrow operator ''%%->%%'' followed by a set of square brackets ''%%[…]%%'' containing a comma-separated list of property name equals ''%%=%%'' expression.
-A trailing comma is permitted for the same reasons it's permitted in array literals and function calls (as of PHP 7.3).
+The proposed syntax consists of the object arrow operator followed by a set of square brackets containing a comma-separated list of assignments in the form of property name equals expression:
-The whole block is considered an expression that returns the object we started with.
+<code>
+<object-expression> -> [
+    `<property-name> = <expression>`,
+    [repeat as needed],
+]
+</code>
+> A trailing comma is permitted for the same reasons it's permitted in array literals and [[https://wiki.php.net/rfc/trailing-comma-function-calls|function calls (as of PHP 7.3)]].
+The whole block is considered an expression that returns the object before the arrow.
+This syntax was chosen for its availability in the language. If we land on another syntax, I’m not married to this one. The only criteria are that it doesn’t conflict with anything else, that it is trivial to implement, brief and feels ok.
 ==== Interpretation ====
-Each comma-separated assignment inside the brackets is executed as an assignment of the named property on the object preceding the block. If the property is defined and publicly accessible, it will simply be set, or possible throw a TypeError. If there's no property with that name, or if it's protected or private, the magic method ''%%__set%%'' will be called just like you would expect.
-When used in an expression, COPA simply returns the object itself.
-==== Use cases ====
+Each comma-separated assignment inside the brackets is executed as an assignment of the named property on the object preceding the block. If the property is defined and publicly accessible, it will simply be set, or possible throw a ''%%TypeError%%''. If there's no property with that name, or if it's protected or private, the magic method ''%%__set%%'' will be called just like you would expect. When used in an expression, **COPA** simply returns the object itself.
-=== DTOs - data transfer objects ===
+If you replace COPA with single line assignments, you will always get the same result, f.ex.:
-Typical features of DTOs:
-  * many properties
-  * properties may be optional, with default values
-  * public visibility on properties, no need for boilerplate code to create setters and getters for each one
-== With current syntax ==
 <code php>
-class Dto {
+$foo->[
-    public string $foo;
+    a = 1,
-    public int $bar = 1; // Optional, with default
+    b = myfunc(),
-    public string $baz;
+    c = $foo->bar(),
-}
+];
-$myDto = new Dto(); // Instantiating the object first
-$myDto->foo = 'get'; // Setting the properties
-$myDto->baz = 'life';
-myFunc($myDto); // Passing to a function
+// The COPA above is identical to
+$foo->a = 1;
+$foo->b = myfunc();
+$foo->c = $foo->bar();
 </code>
+==== Use cases ====
+=== Create and send struct ===
-== With new syntax ==
 <code php>
-myFync((new Dto())->[ // Constructing and populating inline
+// Instead of this:
-    foo = 'get',
-    baz = 'life',
+$myObj = new Foo; // 1. Create struct-like object without constructor arguments
+$myObj->a = 1; // 2. Populate public properties
+$myObj->b = 2;
+$myObj->c = 3;
+doTheFoo($myObj); // 3. Send or process
+// Use COPA:
+doTheFoo((new Foo)->[
+    a = 1,
+    b = 2,
+    c = 3,
 ]);
 </code>
+//No boilerplate needed.//
-=== Argument bags ===
+=== Stop using arrays ===
-Argument bags are typically used when:
-  * many arguments needs to be passed to a function
-  * some arguments are optional
-  * order of arguments is not important
-With the proposed COPA syntax we can avoid using simple arrays and instead get autocomplete and type-checking in the IDE with a syntax that smells of named parameters:
-== With current syntax ==
 <code php>
-class Foo {
+// Instead of this:
-    protected string $foo;
-    protected int $bar;
-    protected string $baz;
-    public function __construct(array $options) {
+doSomething([
-        $this->foo = $options['foo'];
+    'a' => 1, // Anonymous array doesn't provide any help on parameter names
-        $this->bar = $options['bar'] ?? 1;
+    'b' => 2, // or types
-        $this->baz = $options['baz'];
+]);
-    }
+// Use COPA:
+class Options { // Give the data a signature, a well-defined structure
+    public $a;
+    public $b;
 }
-$myFoo = new Foo([
+doSomething((new Options)->[
-    'foo' => 'get', // Array syntax argument bag doesn't provide any help on parameter names
+    a = 1, // Parameter name and type checking
-    'baz' => 'life', // or types
+    b = 2,
 ]);
 </code>
+//If you often create, populate and send the same families of data structure, declaring those structures and using COPA makes it a breeze.//
-== Alternatively, with current syntax ==
+=== Nested COPA ===
-<code php>
-class Foo {
-    protected string $foo;
-    protected int $bar;
-    protected string $baz;
-    public function __construct(string $foo, int $bar, string $baz) {
+COPA is not limited to a flat structure.
-        $this->foo = $foo;
-        $this->bar = $bar;
-        $this->baz = $baz;
-    }
-}
-$myFoo = new Foo('get', 1, 'life'); // Dealing with optional parameters and default values is not straight forward
+<code php>
+(new Foo)->[
+    om = 'get',
+    mane = 'a',
+    hum = (new Foo)->[
+        mane = 'life',
+    ],
+];
 </code>
+=== Split options from services ===
+Separate concerns and use composition. In this example, once you have instantiated Foo, the options are no longer writeable, even though the options were public properties.
-== With new syntax ==
 <code php>
-class FooOptions { // Separate concerns into an options class that handles optional and default values...
+class FooOptions {
-    public string $foo;
+    public ?string $mane = null;
-    public int $bar = 1; // Optional, with default
+    public int $padme = 1; // Optional, with default
-    public string $baz;
+    public ?string $hum = null;
 }
-class Foo { // And the main class that receives the options and handles some feature
+class Foo {
     protected FooOptions $options;
     public function __construct(FooOptions $options) {
-        $this->options = $options;
+        // Do some validate here if you must, f.ex. checking for mandatory parameters
+        $this->options = clone $options;
     }
 }
-$myFoo = new Foo((new FooOptions())->[ // Objects as argument bags smells like named parameters
+$myFoo = new Foo((new FooOptions)->[
-    foo = 'get', // Parameter name and type checking
+    mane = 'get',
-    baz = 'life',
+    hum = 'life',
 ]);
 </code>
+//If you can’t wait for “named parameters” and often resort to “parameter bags” this is a perfectly valid and saner alternative.//
 ==== Special cases ====
+Clarification of edge-case behavior.
 === Execution order ===
-The fact that the assignments are executed in the order they are listed, just as if they had been specified on separate lines, has the following consequence:
+The fact that the assignments are executed in the order they are listed (just as if they had been specified on separate lines), has the following consequence:
 <code php>
 $myObj->[
@@ Line 164: / Line 204: @@
 var_dump($myObj->bar); // int(30)
 </code>
+> As the assignments are carried out in order on the object, you can use the new value of a previous assigment in a following one.
-//There may be arguments equally for and against this behavior, but ultimately the simplicity of the design and implementation wins, in my opinion.//
+=== Exceptions ===
-=== Expressions in property names ===
+If an expression inside a COPA block throws an exception, the result is the same as if the assignments had been done the old way, f.ex. if we have:
-Property names must be expressed literally. Some examples of what's possible in a regular assignment, but won't be allowed inside COPA:
+<code php>
+class Foo {
+    public $a;
+    public $b;
+    public $c;
+}
+$foo = new Foo();
+function iThrow() {
+    throw new \Exception();
+}
+</code>
+Then the following examples behave identically:
+<code php>
+// With COPA:
+try {
+    $foo->[
+        a = 'a',
+        b = iThrow(),
+        c = 'c',
+    ];
+} catch (\Throwable $e) {
+    var_dump($foo);
+}
+</code>
+<code php>
+// Without COPA:
+try {
+    $foo->setA('a')
+        ->setB(iThrow())
+        ->setC('c');
+} catch (\Throwable $e) {
+    var_dump($foo);
+}
+// OR
+try {
+    $foo->a = 'a';
+    $foo->b = iThrow();
+    $foo->c = 'c';
+} catch (\Throwable $e) {
+    var_dump($foo);
+}
+</code>
+The result in all cases is that ''%%a%%'' will be set, while ''%%b%%'' and ''%%c%%'' will not:
+<code>
+object(Foo)#1 (3) {
+  ["a"]=>
+  string(1) "a"
+  ["b"]=>
+  NULL
+  ["c"]=>
+  NULL
+}
+</code>
+> COPA is **not** an atomic operation in the same way that method chaining isn’t.
+==== Out of scope / future scope ====
+This section contains features that is not considered for implementation in version 1 of COPA but may be considered later.
+=== You can’t do that ===
+The following examples show various things that are currently possible when using regular property accessor, though they won’t work inside a COPA block:
 <code php>
 $p = 'foo';
 $myObj->$p = 'bar'; // Variable property name
-$a->{"foo"} = 'baz'; // Property name generated from expression
+$a->{"fo" . "o"} = 'baz'; // Property name generated from expression
+$a->b->c = 'hum'; // Creating default object from empty value
+$a->d['e'] = 'dear'; // Setting array element inside property
+$a->f++; // Increment/decrement of property value
 $myObj->[
     $p = 'bar', // Syntax error
     {"foo"} = 'bar', // Syntax error
+    b->c = 'hum', // Syntax error - but see Nested COPA below...
+    d['e'] = 'dear', // Syntax
+    f++, // Syntax error
 ];
 </code>
+//These can be implemented in the future if there is a demand.//
-//Supporting these expressions would probably be tricky to implement because the property names are not quoted, so they are not represented as literal strings, which makes them look like constants and complicates parsing in general, I believe. It also defeats the purpose of name and type checking, and is not a feature you'd miss in object literals either.//
+=== Nested COPA on existing objects ===
-===== Anti-proposal =====
+The following syntax could be supported in the future:
-This proposal is related to previous RFCs and shares motivation with them. However, there are distinctions and though COPA claims to be in the same family, here are some disclaimers:
-==== This is NOT json ====
+<code php>
-This is not a way to write object literals using JavaScript Object Notation. It's similar to an array literal, but with each key actually corresponding to a defined property of the object. We don't want to quote the property names as there's no advantage, only added overhead. The equals sign is used straightforwardly to denote assignment. Square brackets have been chosen instead of curly ones because the latter already has an interpretation when following the object arrow, namely to create an expression which will return a property or method name.
+// This example, using current syntax...
-  * https://wiki.php.net/rfc/objectarrayliterals
-==== This is NOT object initializer ===
+$foo->a = 1;
-I call this pseudo object literal notation because we're not writing the actual inner state of the object, we're merely populating properties after construction. But this syntax will allow you get benefits very similar to object literals in a simple, pragmatic way.
+$foo->b->c = 2;
-  * https://wiki.php.net/rfc/object-initializer
-==== This is NOT named parameters ====
+// Could be written with COPA like this:
-Though on the wish list since 2013, named parameters have proved a tough nut to crack. But with this RFC you will be able to create parameter objects that may give you benefits very similar to named parameters when you pass it to a function that expects it.
-  * https://wiki.php.net/rfc/named_params
-  * https://wiki.php.net/rfc/simplified_named_params
+$foo->[
+    a = 1,
+    b->[
+        c = 2,
+    ],
+];
+// But for now you'll have to do this:
+$foo->[
+    a = 1,
+    b = $foo->b->[
+        c = 2,
+    ],
+];
+</code>
 ===== Backward Incompatible Changes =====
-None. Array followed by square bracket causes syntax error in PHP 7.4.
-This new syntax is optional. If you don't use it, your code will continue to run.
+None.
+> **Note!** Array followed by square bracket causes syntax error in PHP 7.4. This new syntax is optional. If you don't use it, your code will continue to run.
 ===== Proposed PHP Version(s) =====
-Next PHP 8.x
+PHP 8.0
 ===== Open Issues =====
-===== Proposed Voting Choices =====
+==== Alternative syntaxes ====
+I’m going to suggest some alternative syntaxes, which we can vote on, provided their feasibility has been vetted by an experienced internals developer:
+=== Syntax A ===
+This is the originally proposed one:
+<code php>
+$foo->[
+    a = 1,
+    b = 2,
+    c = (new Foo)->[
+        a = 3,
+        b = 4,
+    ],
+];
+</code>
+=== Syntax B ===
+Since the [[https://wiki.php.net/rfc/deprecate_curly_braces_array_access|deprecation of curly brackets as array access in PHP 7.4]], that notation could be used to assign properties:
+<code php>
+$foo{
+    a = 1,
+    b = 2,
+    c = (new Foo){
+        a = 3,
+        b = 4,
+    },
+};
+</code>
+> Going from deprecation in 7.4 to removal of support in 8.0 may is not unprecedented. Old code that has not been mended won’t silently do something spurious.
+=== Syntax C ===
+No wrapper:
+<code php>
+$foo->
+    a = 1,
+    b = 2,
+    c = (new Foo)->
+        a = 3,
+        b = 4,
+    ;,
+;
+</code>
+Nesting becomes awkward - how do we jump out again?
+> **Note!** This looks more like a chain of normal assignments, but that can be confusion since those normally return the value assigned, not the object itself.
+=== Syntax D ===
+Repeating the arrow for familiarity with regular property assignment:
+<code php>
+$foo
+    ->a = 1,
+    ->b = 2,
+    ->c = (new Foo)
+        ->a = 3,
+        ->b = 4,
+    ;,
+;
+</code>
+Same issues as previous.
+=== Syntax E ===
+Like the original but with normal brackets instead of square ones:
+<code php>
+$foo->(
+    a = 1,
+    b = 2,
+    c = (new Foo)->(
+        a = 3,
+        b = 4,
+    ),
+);
+</code>
+=== Syntax F ===
+**WITH** syntax
+<code php>
+myObj.with {
+     foo = 10
+     bar = foo + 20
+}
+</code>
+If this is the preferred syntax it will require a new RFC.
+===== Rejected Features =====
+Some suggested features have been rejected due to the fact that COPA aims to be pragmatic, with a trivial implementation and without introducing any new concepts to avoid a combinatorial explosion of complexities in the future.
+==== Mandatory properties ====
+Some have voiced criticism that COPA is of little use without also enforcing mandatory properties to be set.
+**Rowan Tommins:**
+> It seems pretty rare that an object would have no mandatory properties, so saying “if you have a mandatory property, COPA is not for you” is ruling out a lot of uses.
+**Michał Brzuchalski:**
+> This helps to avoid bugs where a property is added to the class but forgot to be assigned it a value in all cases where the class is instantiated and initialized
+Mandatory properties are typed properties without a default value. They are in the uninitialized state until they are assigned a value. It has been suggested that an exception should be thrown at the end of the constructor if any property is still uninitialized, but this idea has not yet caught on. COPA doesn’t have any obvious way of enforcing mandatory properties.
+> COPA won’t support this since COPA doesn’t introduce any new concepts or complexities. The lack of this feature is not a limitation of COPA when compared to current functionality.
+//For now you must continue to write your own validation code to be carried out at the appropriate “point of no return”.//
+==== Atomic operations ====
+It’s also been suggested that assigning multiple values using COPA should be an atomic operation that either succeeds or fails in its entirety (i.e. like a “transaction”).
+Though that sounds cool, this is an edge case that won’t have any significant impact. If you were planning to resume gracefully with an incomplete object you should probably reconsider your goals in life.
+> **Note!** Chaining method calls is not an atomic operation either. The cost/benefit of implementing “transaction” and “rollback” behavior is negative.
+===== Vote =====
+Voting starts 2020-03-31 and ends 2020-04-13.
+The primary vote of whether or not to accept this RFC requires a 2/3 majority.
+<doodle title="Would you like to add support for COPA?" auth="jgivoni" voteType="single" closed="true">
+   * Yes
+   * No
+</doodle>
+\\
+<doodle title="If you voted no, what was the main reason?" auth="jgivoni" voteType="single" closed="true">
+   * I voted yes!
+   * I don’t find the feature useful
+   * I don’t like the syntax
+   * I prefer a more comprehensive solution to this problem
+   * I prefer a narrower solution to this problem
+   * This breaks backwards compatibility
+   * This will have negative implications for future language evolution
+   * This will be a nightmare to implement and maintain
+   * I prefer not to say
+</doodle>
+\\
+<doodle title="If you did not like the proposed syntax, which alternative would you prefer?" auth="jgivoni" voteType="single" closed="true">
+   * A (the proposed one)
+   * B
+   * C
+   * D
+   * E
+   * F
+   * Irrelevant
+</doodle>
 ===== Patches and Tests =====
 There are yet no patches nor tests. The question of who will be developing this will be addressed if the RFC passes.
 ===== Implementation =====
-After the project is implemented, this section should contain
+After the project is implemented, this section should contain
   - the version(s) it was merged into
   - a link to the git commit(s)
@@ Line 221: / Line 516: @@
 ===== References =====
+Related RFCs:
   * https://wiki.php.net/rfc/object-initializer
   * https://wiki.php.net/rfc/objectarrayliterals
   * https://wiki.php.net/rfc/simplified_named_params
   * https://wiki.php.net/rfc/named_params
+  * https://wiki.php.net/rfc/code_free_constructor
-===== Rejected Features =====
+  * https://wiki.php.net/rfc/constructor-promotion
+  * https://wiki.php.net/rfc/automatic_property_initialization
+  * https://wiki.php.net/rfc/skipparams

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