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* perf: optimize Substring to work directly with strings instead of converting to runes
- Rewrite Substring to iterate over string bytes directly, avoiding full []rune conversion
- Improve performance for long strings by only processing necessary portions
- Add comprehensive test cases for Unicode handling, invalid UTF-8, and edge cases
- Add BenchmarkSubstring to measure performance improvements
- Improve documentation with detailed parameter descriptions
- Handle invalid UTF-8 sequences by converting to []rune when needed
Bencstat:
│ old.txt │ new.txt │
│ sec/op │ sec/op vs base │
Substring/{10_10}-4 558.85n ± 9% 39.75n ± 10% -92.89% (p=0.000 n=8)
Substring/{50_50}-4 783.10n ± 6% 85.15n ± 5% -89.13% (p=0.000 n=8)
Substring/{50_45}-4 773.30n ± 3% 126.5n ± 7% -83.65% (p=0.000 n=8)
Substring/{-50_50}-4 794.00n ± 2% 177.6n ± 7% -77.63% (p=0.000 n=8)
Substring/{-10_10}-4 542.85n ± 20% 41.82n ± 6% -92.30% (p=0.000 n=8)
geomean 680.4n 79.52n -88.31%
│ old.txt │ new.txt │
│ B/op │ B/op vs base │
Substring/{10_10}-4 432.0 ± 0% 0.0 ± 0% -100.00% (p=0.000 n=8)
Substring/{50_50}-4 480.0 ± 0% 0.0 ± 0% -100.00% (p=0.000 n=8)
Substring/{50_45}-4 464.0 ± 0% 0.0 ± 0% -100.00% (p=0.000 n=8)
Substring/{-50_50}-4 480.0 ± 0% 0.0 ± 0% -100.00% (p=0.000 n=8)
Substring/{-10_10}-4 432.0 ± 0% 0.0 ± 0% -100.00% (p=0.000 n=8)
│ old.txt │ new.txt │
│ allocs/op │ allocs/op vs base │
Substring/{10_10}-4 2.000 ± 0% 0.000 ± 0% -100.00% (p=0.000 n=8)
Substring/{50_50}-4 2.000 ± 0% 0.000 ± 0% -100.00% (p=0.000 n=8)
Substring/{50_45}-4 2.000 ± 0% 0.000 ± 0% -100.00% (p=0.000 n=8)
Substring/{-50_50}-4 2.000 ± 0% 0.000 ± 0% -100.00% (p=0.000 n=8)
Substring/{-10_10}-4 2.000 ± 0% 0.000 ± 0% -100.00% (p=0.000 n=8)
* Enhance substring documentation with Unicode details
Returns a substring starting at the given offset with the specified length. Supports negative offsets; out-of-bounds are clamped. Operates on Unicode runes (characters) and is optimized for zero allocations.
---------
Co-authored-by: Samuel Berthe <dev@samuel-berthe.fr>
55 lines
1.4 KiB
Markdown
55 lines
1.4 KiB
Markdown
---
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name: Substring
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slug: substring
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sourceRef: string.go#L105
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category: core
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subCategory: string
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playUrl: https://go.dev/play/p/TQlxQi82Lu1
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variantHelpers:
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- core#string#substring
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similarHelpers:
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- core#string#chunkstring
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- core#string#runelength
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- core#string#ellipsis
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- core#string#words
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- core#slice#replace
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- core#slice#replaceall
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position: 10
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signatures:
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- "func Substring[T ~string](str T, offset int, length uint) T"
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---
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Returns a substring starting at the given offset with the specified length. Supports negative offsets; out-of-bounds are clamped. Operates on Unicode runes (characters) and is optimized for zero allocations.
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```go
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// Basic usage
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result := lo.Substring("hello", 2, 3)
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// result: "llo"
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// Negative offset - counts from end
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result = lo.Substring("hello", -4, 3)
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// result: "ell"
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// Length longer than string - clamped to available characters
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result = lo.Substring("hello", 1, 10)
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// result: "ello" (only 4 characters available from position 1)
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// Zero length - returns empty string
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result = lo.Substring("hello", 1, 0)
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// result: ""
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// Offset beyond string length - returns empty string
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result = lo.Substring("hello", 10, 3)
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// result: ""
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// With Unicode strings (rune-aware)
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result = lo.Substring("héllo", 1, 3)
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// result: "él"
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// Negative offset with negative values clamped
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result = lo.Substring("hello", -10, 3)
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// result: "hel" (offset clamped to 0)
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```
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