Use "singleton type" instead of "value type" (#4332)

Author: kamil-tekiela

language/types.xml

@@ -131,7 +131,7 @@ int(16)
  &language.types.void;
  &language.types.never;
  &language.types.relative-class-types;
- &language.types.value;
+ &language.types.singleton;
  &language.types.iterable;
  &language.types.declarations;
  &language.types.type-juggling;

language/types/declarations.xml

@@ -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 singleton types <type>false</type>
      and <type>true</type> together in a union type.
      Use <type>bool</type> instead.
     </simpara>

language/types/value.xml renamed to language/types/singleton.xml

@@ -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.singleton">
+ <title>Singleton 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>
+  Singleton types are those which allow only one value.
+  PHP has support for two singleton types:
+  <type>false</type> as of PHP 8.0.0 and <type>true</type>
   as of PHP 8.2.0.
  </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> 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 singleton types. Consider using an
    <link linkend="language.types.enumerations">enumerations</link> instead.
   </simpara>
  </note>

language/types/type-system.xml

@@ -27,9 +27,6 @@
     <listitem>
      <simpara>Built-in types</simpara>
      <itemizedlist>
-      <listitem>
-       <simpara><type>null</type> type</simpara>
-      </listitem>
       <listitem>
        <simpara>
         Scalar types:
@@ -70,18 +67,28 @@
         <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>
+       <simpara>
+        <link linkend="language.types.singleton">Singleton types</link>
+       </simpara>
+       <itemizedlist>
+        <listitem>
+         <simpara><type>false</type></simpara>
+        </listitem>
+        <listitem>
+         <simpara><type>true</type></simpara>
+        </listitem>
+       </itemizedlist>
       </listitem>
       <listitem>
-       <simpara><type>true</type></simpara>
+       <simpara>
+        Unit types
+       </simpara>
+       <itemizedlist>
+        <listitem>
+         <simpara><type>null</type></simpara>
+        </listitem>
+       </itemizedlist>
       </listitem>
      </itemizedlist>
     </listitem>