Programmer Reference : UnicodeSupport : Utf16View
Utf16View
Description
A Utf16View provides a bidirectional view over the unicode component as a collection of UTF-16 code units in platform-endian format.
UTF-16 is a 16-bit variable-length encoding that encodes unicode scalar values with one or two 16-bit code units. Unicode scalar values < 2^16 can be encoded in one 16-bit code unit, while everything above 2^16 will require two 16-bit code units. This pair of code units is called a surrogate pair with a leading surrogate and a trailing
surrogate.
  • #next/#previous - Answers a 16-bit <Integer>.
  • #contents - Answers a <Utf16>
Examples
| view |
view := Utf16View on: 'abc'.
self assert: [view next = $a value].
self assert: [view next = $b value].
self assert: [view next = $c value].
self assert: [view atEnd].
self assert: [view previous = $c value].
self assert: [view previous = $b value].
self assert: [view previous = $a value].
self assert: [view atStart].
self assert: [view contents asArray = { $a value. $b value. $c value}]
Instance State
  • trailingSurrogate: <Integer | UndefinedObject> vm managed decoder state. Will be notNil if cursored on a surrogate
pair.
  • startAtTrailingSurrogate: <Boolean> vm managed. True if the view's first element is the trailing surrogate of a
surrogate pair.
  • stopAfterLeadingSurrogate: <Boolean> vm managed. True if the view's last element is the leading surrogate of a
surrogate pair.
Class Methods
None
Instance Methods
<details> atEnd
<pre><code>   Answer a Boolean which is true if the receiver cannot    access any more objects, and false otherwise.
   Notes:     Override is required since utf16 views can end on a leading surrogate in a     surrogate pair. Therefore, the view surrogate related state must be considered     before it can be determined that the utf16 view is positioned at the end.         Example:     | view sliceView |     'EARTH GLOBE EUROPE-AFRICA'.     view := #[240 159 140 141] utf16.     self assert: [view contents = (Utf16 with: 55356 with: 57101)].          sliceView := view copyFrom: 1 to: 1.     self assert: [sliceView contents = (Utf16 with: 55356)].     self assert: [sliceView atEnd not].     self assert: [sliceView next = 55356].     self assert: [sliceView atEnd].
    sliceView := view copyFrom: 2.     self assert: [sliceView contents = (Utf16 with: 57101)].     self assert: [sliceView atEnd not].     self assert: [sliceView next = 57101].     self assert: [sliceView atEnd]         Answers:     <Boolean> </code></pre> </details>
<details> atStart
<pre><code>   Answer a Boolean which is true if the receiver cannot    access any more objects, and false otherwise.   
   Notes:     Override is required since utf16 views can start on a trailing surrogate in a     surrogate pair. Therefore, the view surrogate related state must be considered     before it can be determined that the utf16 view is positioned at the start.
   Example:     | view sliceView |     'EARTH GLOBE EUROPE-AFRICA'.     view := #[240 159 140 141] utf16.     self assert: [view contents = (Utf16 with: 55356 with: 57101)].          sliceView := view copyFrom: 1 to: 1.     self assert: [sliceView contents = (Utf16 with: 55356)].     sliceView setToEnd.     self assert: [sliceView atStart not].     self assert: [sliceView previous = 55356].     self assert: [sliceView atStart].
    sliceView := view copyFrom: 2.     self assert: [sliceView contents = (Utf16 with: 57101)].     sliceView setToEnd.     self assert: [sliceView atStart not].     self assert: [sliceView previous = 57101].     self assert: [sliceView atStart]         Answers:     <Boolean> </code></pre> </details>
Last modified date: 01/18/2023