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util/slicesx: add Filter function
For use in corp, where we appear to have re-implemented this in a few places with varying signatures. Signed-off-by: Andrew Dunham <andrew@du.nham.ca> Change-Id: Id863a87e674f3caa87945519be8e09650e9c1d76
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@ -77,3 +77,17 @@ func EqualSameNil[S ~[]E, E comparable](s1, s2 S) bool {
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}
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return true
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}
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// Filter calls fn with each element of the provided src slice, and appends the
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// element to dst if fn returns true.
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//
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// dst can be nil to allocate a new slice, or set to src[:0] to filter in-place
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// without allocating.
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func Filter[S ~[]T, T any](dst, src S, fn func(T) bool) S {
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for _, x := range src {
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if fn(x) {
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dst = append(dst, x)
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}
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}
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return dst
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}
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@ -97,3 +97,42 @@ func TestEqualSameNil(t *testing.T) {
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c.Check(EqualSameNil([]string{}, nil), qt.Equals, false)
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c.Check(EqualSameNil[[]string](nil, nil), qt.Equals, true)
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}
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func TestFilter(t *testing.T) {
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var sl []int
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for i := 1; i <= 10; i++ {
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sl = append(sl, i)
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}
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evens := Filter(nil, sl, func(elem int) bool {
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return elem%2 == 0
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})
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want := []int{2, 4, 6, 8, 10}
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if !reflect.DeepEqual(evens, want) {
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t.Errorf("evens: got %v, want %v", evens, want)
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}
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}
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func TestFilterNoAllocations(t *testing.T) {
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var sl []int
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for i := 1; i <= 10; i++ {
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sl = append(sl, i)
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}
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want := []int{2, 4, 6, 8, 10}
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allocs := testing.AllocsPerRun(1000, func() {
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src := slices.Clone(sl)
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evens := Filter(src[:0], src, func(elem int) bool {
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return elem%2 == 0
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})
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if !slices.Equal(evens, want) {
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t.Errorf("evens: got %v, want %v", evens, want)
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}
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})
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// 1 alloc for 'src', nothing else
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if allocs != 1 {
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t.Fatalf("got %.4f allocs, want 1", allocs)
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}
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}
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