ecmascript/string

String implementation with multiple string representations (tree, line, sliced, external) and efficient Unicode handling. Primary Language: C++

Design

Multiple string representations for memory efficiency:

  String creation
       │
       ├──▶ TreeString: Binary tree for concatenation
       ├──▶ LineString: Single-line string
       ├──▶ SlicedString: View into parent string
       └──▶ ExternalString: External memory buffer
       │
       ▼
  BaseString (common interface)
       ├── Length, charAt, substring operations
       ├── Hash computation
       └── Comparison and equality

Key abstractions:

• BaseString — Common string interface and base class
• TreeString — Binary tree node with left and right substrings for efficient concatenation
• LineString — Contiguous string data
• SlicedString — Zero-copy substring view
• ExternalString — External memory reference
• BaseStringTable — String interning and deduplication
• IntegerCache — Cached integer string representations

Reference Source

• arkcompiler/ets_runtime/ecmascript/string/base_string.h (1-300行) - Base string interface
• arkcompiler/ets_runtime/ecmascript/string/tree_string.h - Tree string implementation

Key Files

File	Role
base_string.h/.cpp	Base string class and interface
tree_string.h	Tree string for concatenation
line_string.h	Contiguous string data
sliced_string.h	Substring view
external_string.h	External memory string
base_string_table.h/.cpp	String interning
integer_cache.h	Integer string cache
hashtriemap.h	String hash table implementation

Building

Standalone repo (from repo root ../../):

python ark.py x64.debug

Full OHOS tree:

./build.sh --product-name <product-name> --build-target ark_js_host_linux_tools_packages

Tests

Standalone repo (from repo root ../../):

python ark.py x64.debug unittest   # includes string tests

Full OHOS tree:

./build.sh --product-name <product-name> --build-target ecmascript/string/tests:host_unittest

Boundaries

• String representations are immutable; mutations create new strings.
• TreeString is a binary tree, not balanced; character access traverses left/right subtrees.
• TreeString is flat if right substring is empty; enables flattening optimization.
• ExternalString lifetime management is caller's responsibility.
• Unicode handling follows ECMAScript spec (UTF-16 code units).