as-string-sink

String Sink

An efficient dynamically sized string buffer (aka String Builder) for AssemblyScript.

Interface

class StringSink {
  static withCapacity(capacity: i32)

  constructor(initial: string = "", capacity: i32 = 32)

  get length(): i32
  get capacity(): i32

  write(src: string, start?: i32, end?: i32): void
  writeLn(src: string, start?: i32, end?: i32): void
  writeCodePoint(code: i32): void

  reserve(capacity: i32, clear?: bool): void
  shrink(): void
  clear(): void

  toString(): string
}

Benchmark Results

StringSink can be up to 8700 times faster than native string concatenation!

100 strings:
------------
String += JS:  0.013 ms
String += AS:  0.017 ms
StringSink AS: 0.0034 ms

50,000 strings:
---------------
String += JS:  3.89 ms
String += AS:  1219.44 ms
StringSink AS: 0.54 ms

200,000 strings:
----------------
String += JS:  11.29 ms
String += AS:  18360.15 ms
StringSink AS: 2.28 ms

Usage 1. String accumulation (+=)

non efficient example:

function toList(arr: string[]): string {
  let res = "";
  for (let i = 0, len = arr.length; i < len; i++) {
    res += arr[i] + "\n";
  }
  return res;
}

efficient with StringSink:

function toList(arr: string[]): string {
  let res = new StringSink();
  for (let i = 0, len = arr.length; i < len; i++) {
    res.write(arr[i] + "\n");
  }
  return res.toString();
}

even more efficient:

function toList(arr: string[]): string {
  let res = new StringSink();
  for (let i = 0, len = arr.length; i < len; i++) {
    res.writeLn(arr[i]);
  }
  return res.toString();
}

Usage 2. String accumulation (+=) only part of string

non efficient example:

function toListSliced(arr: string[]): string {
  let res = "";
  for (let i = 0, len = arr.length; i < len; i++) {
    res += arr[i].substring(1, 3);
  }
  return res;
}

more efficient with StringSink:

function toListSliced(arr: string[]): string {
  let res = new StringSink();
  for (let i = 0, len = arr.length; i < len; i++) {
    res.write(arr[i], 1, 3);
  }
  return res.toString();
}