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Date: Wed, 1 Jun 2016 12:15:44 +1000
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Subject: Set object properties inline
From: me@jesseschalken.com (Jesse Schalken)

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Hi internals,

I often have code dealing with plain old PHP objects with properties and no
methods, either as a substitute for keyword arguments, or to represent a
JSON or YAML document for a web service, configuration file or schemaless
database.

At the moment, instantiating an object and setting public properties
requires a temporary variable for each object in the structure:

$obj1 = new Obj1();
$obj1->prop1 = ...;
$obj1->prop2 = ...;

$params = new FooParams();
$params->prop1 = ..;
$params->prop2 = ...;
$params->prop3 = $obj1;

$this->fooMethod($arg1, $arg2, $params);


For large structures, this gets verbose very quick. There is a good example
of this here
<https://github.com/jesseschalken/fail-whale/blob/72870b37c4c21d19f17324a966344ec476b432a7/src/FailWhale/Introspection.php#L22>
involving
18 unnecessarily variables.

I can remove the local variables by defining setters for all the properties:

$this->fooMethod(

    $arg1,
    $arg2,
    (new FooParams())

        ->setProp1(...)

        ->setProp2(...)

        ->setProp3((new Obj1())

        ->setProp1(...)

        ->setProp2(...))

);


But now for each property I have to spend an extra 3-5 lines of code
defining a setter, which is more code than it saved (unless the class is
used heavily enough).

I could define __construct() taking every property as a parameter, but then
each property has to be mentioned another three times (four times with a
doc comment), and the type twice:

class FooParams {

    public int $prop1;
    // ...


    public function __construct(
        int $prop1
        // ...
    ) {

        $this->prop1 = $prop1;
        // ...

    }

}


and where the object is constructed, it isn't immediately visible what the
meaning of each positional parameter is without some IDE assistance (eg
Ctrl+P in PhpStorm), and only specifying some parameters requires filling
preceding ones with defaults.

I could also define the __call() method to automatically expose setters,
but then IDEs and static analysis can't understand what's going on (it
can't see that those methods exist, what their parameters are and what they
return). @method doc comments on the class help, but that's another line
for every property which I have to manually keep in sync with the real
properties.

It would be great if there was a simple shorthand syntax for setting
properties on an object in-line, without needing to extract a variable:

$this->fooMethod(
    $arg1,
    $arg2,
    new FooParams() {
        prop1 = ...,
        prop2 = ...,
        prop3 = new Obj1() {
            prop1 = ...,
            prop2 = ...,
        },
    }
);


This way the structure can be written directly in the code as an expression
and FooParams and Obj1 remain simple containers for properties.

The grammar might look like (I haven't used bison/yacc before):

expr_without_variable:
        /* ... */
    |   expr '{' inline_set_properties '}'
;

inline_set_properties:
        /* empty */
    |   identifier '=' expr
    |   identifier '=' expr ',' inline_set_properties
;


(Although I think that would conflict with the alternative $var{8} syntax
for array/string offset.)

Has this been explored before? What problems can you foresee (or have been
foreseen) with such a feature?

Thanks

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