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Use "unit type" instead of "value type" #4332

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Use "unit type" instead of "value type" #4332

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0704534
Use "unit type" instead of "value type"
kamil-tekiela Dec 21, 2024
2c50802
unit => singleton
kamil-tekiela Jan 15, 2025
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2 changes: 1 addition & 1 deletion language/types.xml
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Original file line number Diff line number Diff line change
Expand Up @@ -131,7 +131,7 @@ int(16)
&language.types.void;
&language.types.never;
&language.types.relative-class-types;
&language.types.value;
&language.types.unit;
&language.types.iterable;
&language.types.declarations;
&language.types.type-juggling;
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2 changes: 1 addition & 1 deletion language/types/declarations.xml
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Expand Up @@ -271,7 +271,7 @@ Stack trace:
<title>Union types</title>
<warning>
<simpara>
It is not possible to combine the two value types <type>false</type>
It is not possible to combine the two unit types <type>false</type>
and <type>true</type> together in a union type.
Use <type>bool</type> instead.
</simpara>
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28 changes: 14 additions & 14 deletions language/types/type-system.xml
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Expand Up @@ -27,9 +27,6 @@
<listitem>
<simpara>Built-in types</simpara>
<itemizedlist>
<listitem>
<simpara><type>null</type> type</simpara>
</listitem>
<listitem>
<simpara>
Scalar types:
Expand Down Expand Up @@ -70,18 +67,21 @@
<type>self</type>, <type>parent</type>, and <type>static</type>
</simpara>
</listitem>
</itemizedlist>
</listitem>
<listitem>
<simpara>
<link linkend="language.types.value">Value types</link>
</simpara>
<itemizedlist>
<listitem>
<simpara><type>false</type></simpara>
</listitem>
<listitem>
<simpara><type>true</type></simpara>
<simpara>
<link linkend="language.types.unit">Unit types</link>
</simpara>
<itemizedlist>
<listitem>
<simpara><type>false</type></simpara>
</listitem>
<listitem>
<simpara><type>true</type></simpara>
</listitem>
<listitem>
<simpara><type>null</type></simpara>
</listitem>
</itemizedlist>
</listitem>
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I disagree with this change, since gettype(false) returns boolean. Thus the boolean type is not simply the union of the true and the false type, but an independent type.

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I don't think I made that claim anywhere in this PR. What exactly in this PR do you disagree with? Your comment points to the lines where I changed "Value type" to "Unit type", added a null entry and indented the list to be inside of "Built-in types". I don't think either one of these makes it seem as if boolean is a union of false and true.

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@TimWolla TimWolla Jan 10, 2025 •
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I don't think either one of these makes it seem as if boolean is a union of false and true.

My reasoning goes like this:

  • Any given value can have only one type.
  • A unit type can contain only one value.
  • gettype(false) indicates that the value false is of type boolean.
  • That means it cannot be of type false.
  • That means that the type false has no members.
  • That means that the type false cannot actually exist as a unit type.

What exactly in this PR do you disagree with?

Effectively the entire PR, but here it becomes obvious that calling true and false a unit type does not reflect reality.

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I see what you mean, but that would imply that true and false cannot be used in type specifications as they are not types. And yet, we can write function foo(null $n, false $f, true $t). If we pass a wrong value as an argument we get:

Uncaught TypeError: foo(): Argument #2 ($f) must be of type false, true given

I don't agree with this axiom:

Any given value can have only one type.

Consider the following example:

<?php

class A {
    public function __invoke($x)
    {
        var_dump($x);
    }
}

$a = new A;
var_dump(gettype($a)); // object
var_dump(is_object($a)); // true
var_dump(is_a($a, A::class)); // true
var_dump(is_callable($a)); // true

This value belongs to at least 3 different types.

false and true are subtypes of the bool type.

If the current PR is unsuitable, I am open to suggestions how to document this better.

</itemizedlist>
</listitem>
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17 changes: 9 additions & 8 deletions language/types/value.xml → language/types/unit.xml
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Original file line number Diff line number Diff line change
@@ -1,24 +1,25 @@
<?xml version="1.0" encoding="utf-8"?>
<sect1 xml:id="language.types.value">
<title>Value types</title>
<sect1 xml:id="language.types.unit">
<title>Unit types</title>

<para>
Value types are those which not only check the type of a value but also
the value itself. PHP has support for two value types:
<type>false</type> as of PHP 8.0.0, and <type>true</type>
as of PHP 8.2.0.
Unit types are those which allow only one value.
PHP has support for three unit types:
<type>false</type> as of PHP 8.0.0, <type>true</type>
as of PHP 8.2.0, and <type>null</type>.
</para>

<warning>
<simpara>
Prior to PHP 8.2.0 the <type>false</type> type could only be used as part of a
Prior to PHP 8.2.0 the <type>false</type> and <type>null</type> type
could only be used as part of a
<link linkend="language.types.type-system.composite.union">union type</link>.
</simpara>
</warning>

<note>
<simpara>
It is not possible to define custom value types. Consider using an
It is not possible to define custom unit types. Consider using an
<link linkend="language.types.enumerations">enumerations</link> instead.
</simpara>
</note>
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