perf(builtin): min, max, mean, median fast paths

[thevilledev]

Motivation

The min, max, mean, and median builtin functions were using reflection for every element in the input array, calling reflect.Value.Index(i).Interface() in a loop. This causes significant allocations (100+ per call for 100 elements) because each .Interface() call triggers heap allocations.

Changes

Avoid reflection and per-element allocations for common typed slices ([]int, []float64, []any) by adding type-switch fast paths that iterate directly without calling reflect.Value.Interface().

Added benchmarks:

• Benchmark_min
• Benchmark_max
• Benchmark_mean
• Benchmark_median

Benchstat results against master branch:

cpu: Apple M1
│ master.out │ fix.out │
│ sec/op │ sec/op vs base │
_min-8 2850.5n ± 0% 427.7n ± 1% -85.00% (p=0.000 n=10)
_max-8 2877.5n ± 1% 443.2n ± 0% -84.60% (p=0.000 n=10)
_mean-8 2140.0n ± 1% 227.2n ± 0% -89.38% (p=0.000 n=10)
_median-8 4.801µ ± 1% 1.360µ ± 1% -71.67% (p=0.000 n=10)
geomean 3.030µ 491.9n -83.76%
│ master.out │ fix.out │
│ B/op │ B/op vs base │
_min-8 1648.00 ± 0% 48.00 ± 0% -97.09% (p=0.000 n=10)
_max-8 1648.00 ± 0% 48.00 ± 0% -97.09% (p=0.000 n=10)
_mean-8 1656.00 ± 0% 56.00 ± 0% -96.62% (p=0.000 n=10)
_median-8 4.391Ki ± 0% 2.047Ki ± 0% -53.38% (p=0.000 n=10)
geomean 2.071Ki 128.2 -93.95%
│ master.out │ fix.out │
│ allocs/op │ allocs/op vs base │
_min-8 102.000 ± 0% 2.000 ± 0% -98.04% (p=0.000 n=10)
_max-8 102.000 ± 0% 2.000 ± 0% -98.04% (p=0.000 n=10)
_mean-8 103.000 ± 0% 3.000 ± 0% -97.09% (p=0.000 n=10)
_median-8 211.00 ± 0% 11.00 ± 0% -94.79% (p=0.000 n=10)
geomean 122.6 3.390 -97.24%

Further comments

Other typed slices (e.g., []int32, []uint64, custom numeric types) fall back to the original reflection-based path. Open to feedback whether we should include more typed slices here.

Similar optimizations could potentially be applied to other builtins like sum.

[antonmedv]

Nice! I like such optimizations!

[thevilledev]

Thanks! So much fun :)

Needs more tests and fine-tuning, but I'll mark it ready once there 🤞