Add shape offsets page

Author: Kirill Nesmeyanov

Writerside/cfg/static/custom.css

@@ -1,3 +1,7 @@
+:root {
+    --wh-color-accent-substrate-bg: #222330 !important;
+}
+
 .article > .prompt {
     max-width: auto !important;
 }
@@ -29,4 +33,4 @@ p + .code-collapse__wrapper,
 
 #mermaid .flowchart-link {
     stroke: #59595c6b !important;
-}
+}

Writerside/tl.tree

@@ -20,8 +20,12 @@
                      toc-title="Shapes"/>
         <toc-element topic="callable-types.md"
                      toc-title="Callables"/>
-        <!-- TODO -->
-        <toc-element topic="conditional-types.md" toc-title="Conditions" hidden="true"/>
+        <toc-element topic="offset-access.md"
+                     toc-title="Offsets"/>
+                        <!-- TODO -->
+        <toc-element topic="conditional-types.md"
+                     toc-title="Conditions"
+                     hidden="true" />
         <toc-element topic="comparison.md"
                      toc-title="Comparison of syntax between different tools" />
 

Writerside/topics/language/basic-types.md

@@ -1,4 +1,5 @@
 # Basic Types
+
 <show-structure for="chapter" depth="2"/>
 
 The parser does not impose restrictions on type naming. The type name must begin

Writerside/topics/language/callable-types.md

@@ -1,4 +1,5 @@
 # Callable Types
+
 <show-structure for="chapter" depth="2"/>
 
 Callable types describe an arbitrary type that describes a function.

Writerside/topics/language/generic-types.md

@@ -1,4 +1,5 @@
 # Generic Types
+
 <show-structure for="chapter" depth="2"/>
 
 Each type can take arguments containing other type declarations. Validation of

Writerside/topics/language/offset-access.md

@@ -0,0 +1,67 @@
+# Type Offsets
+
+<show-structure for="chapter" depth="2"/>
+<secondary-label ref="tl1.4"/>
+
+To specify a reference to a specific <a href="shape-types.md">shape or array element</a>, 
+the offset access syntax is used.
+
+A description of this type consists of two parts: Arbitrary type description; 
+The type of specific element, enclosed in square `[]` brackets.
+
+<tabs>
+<tab title="Examples">
+
+> Type with string key "offset".
+> ```typescript
+> T['offset']
+> ```
+
+> Type with dependent key.
+> ```typescript
+> T[U]
+> ```
+
+> <a href="shape-types.md">Shape type</a> with numeric key.
+> ```typescript
+> array{int, string}[0]
+> ```
+
+> Complex example using <a href="shape-types.md">shape types</a> 
+> and <a href="generic-types.md">generics</a>.
+> ```typescript
+> T<U>[object{key: int, ...}]
+> ```
+
+</tab>
+<tab title="Counterexamples">
+
+> The offset is enclosed in single brackets.
+> ```typescript
+> Collection[[Some]]
+> ```
+> ```
+> Syntax error, unexpected "["
+> ```
+> {collapsible="true" collapsed-title="TypeLang\Parser\Exception\ParseException"}
+> {style="warning"}
+
+> There must be a type description first, followed 
+> by a reference to an element of that type.
+> ```typescript
+> Collection['key']{key: string}
+> ```
+> ```
+> Syntax error, unexpected "{"
+> ```
+> {collapsible="true" collapsed-title="TypeLang\Parser\Exception\ParseException"}
+> {style="warning"}
+
+</tab>
+</tabs>
+
+<note>
+Note that since this is a type description language, any key type is allowed, 
+including objects, <a href="conditional-types.md">conditions</a> or 
+<a href="shape-types.md">shapes</a>.
+</note>

Writerside/topics/language/shape-types.md

@@ -1,14 +1,11 @@
 # Shape Types
+
 <show-structure for="chapter" depth="2"/>
 
 Each **composite** type can be rigidly described by a structural type called a
 "shape". A shape within the PHP language can be applied to any array or object
 and contain either implicit or explicit keys.
 
-> Support for other types of **keys**, such as const mask (`Class::CONST_*)` 
-> is not currently available.
-{style="warning"}
-
 <tabs>
 <tab title="named explicit keys">
 
@@ -62,6 +59,19 @@ array{
 > {collapsible="true" collapsed-title="TypeLang\Parser\Exception\ParseException"}
 {style="warning"}
 
+> Support for other types of **keys**, such as const mask (`Class::CONST_*`)
+> is not currently available.
+> ```php
+> array{
+>     Class::CONST_*: string,
+>     ...
+> }
+> ```
+> ```
+> Syntax error, unexpected ":"
+> ```
+> {collapsible="true" collapsed-title="TypeLang\Parser\Exception\ParseException"}
+{style="warning"}
 
 ### Unsealed Shapes