mirror of
https://github.com/vercel-labs/scriptc.git
synced 2026-10-24 06:14:01 +08:00
Chris Tate
416311f2c5
The runtime appends to a string in place when the left operand is uniquely owned, but three common forms never got there: - `obj.field += s` on a plain class or record field kept a second reference to the old value, so every append copied the whole string. The compound assignment now reads a stored string field into a mutable local, stores "" into the field (no code runs in between: both operands are already strings), runs the self-append `old = old + rhs` and stores the result. - `s = s + a + b` copied per append: the self-append recognized only `s = s + x`. A concat chain whose leftmost operand is the target now takes the remaining operands as the suffix, in the same order. - `s += String.fromCharCode(c)` built a one-character string first. scr_str_concat_move_char_code appends the character, in place for ASCII. Self-appends also borrow the suffix instead of retaining it, and a discarded compound assignment no longer retains and releases its result.
38 lines
1.5 KiB
TypeScript
38 lines
1.5 KiB
TypeScript
// `s += String.fromCharCode(c)` appends one character: ASCII, two- and
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// three-byte characters, surrogate halves that join into one character,
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// codes that wrap modulo 2^16, aliases of the old string (which must not
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// change), and growth from an empty string, against Node.
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let s = "";
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const seen: string[] = [];
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for (let i = 0; i < 1000; i++) {
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s += String.fromCharCode(32 + (i % 95));
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if (i % 250 === 0) seen.push(s);
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}
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console.log(s.length, s.slice(0, 10), s.slice(-10), seen.map((x) => x.length).join(","));
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let t = "abc";
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const alias = t;
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t += String.fromCharCode(100);
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t += String.fromCharCode(0xe9);
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t += String.fromCharCode(0x65e5);
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t += String.fromCharCode(0x10041);
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t += String.fromCharCode(-1);
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console.log(t, t.length, alias, alias.length);
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let pair = "x";
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pair += String.fromCharCode(0xd83d);
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const half = pair;
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pair += String.fromCharCode(0xde00);
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console.log(pair, pair.length, half.length, half.charCodeAt(1).toString(16));
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let lone = "";
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lone += String.fromCharCode(0xde00);
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lone += String.fromCharCode(0xd83d);
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console.log(lone.length, lone.charCodeAt(0).toString(16), lone.charCodeAt(1).toString(16));
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let codes = "";
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for (const c of [72, 101, 108, 108, 111, 1.9, 65.5, 0x7f, 0x80]) codes += String.fromCharCode(c);
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console.log(JSON.stringify(codes), codes.length);
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function build(n: number): string {
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let out = "";
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for (let i = 0; i < n; i++) out += String.fromCharCode(97 + (i % 26));
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return out;
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}
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console.log(build(0), build(1), build(27), build(5000).length);
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