Add examples for KDTree and enable errcheck linter in CI

.github/workflows/ci.yml

@@ -21,6 +21,7 @@ jobs:
         uses: actions/setup-go@v5
         with:
           go-version: ${{ matrix.go-version }}
+          cache: true
 
       - name: Go env
         run: go env

.golangci.yml

@@ -8,13 +8,22 @@ linters:
     - ineffassign
     - gofmt
     - revive
+    - errcheck
 issues:
   exclude-use-default: false
   max-issues-per-linter: 0
   max-same-issues: 0
+  exclude-rules:
+    # Errcheck is noisy in examples and doc tests; ignore *_test.go for errcheck only.
+    - path: _test\.go
+      linters:
+        - errcheck
 linters-settings:
   revive:
     severity: warning
     rules:
       - name: exported
         arguments: ["disable"] # keep comments pragmatic; we have pkg docs and key API docs
+  errcheck:
+    # Be pragmatic: don't require checking of Close for defer patterns in tests/examples.
+    # (Keep defaults; exclusions above handle test files.)

CHANGELOG.md

@@ -5,6 +5,10 @@ All notable changes to this project will be documented in this file.
 The format is based on Keep a Changelog and this project adheres to Semantic Versioning.
 
 ## [Unreleased]
+### Added
+- pkg.go.dev Examples: `ExampleNewKDTreeFromDim_Insert`, `ExampleKDTree_TiesBehavior`, `ExampleKDTree_Radius_none`.
+- Lint: enable `errcheck` in `.golangci.yml` with test-file exclusion to reduce noise.
+- CI: enable module cache in `actions/setup-go` to speed up workflows.
 
 ## [0.2.1] - 2025-11-03
 ### Added

examples_test.go

@@ -163,3 +163,38 @@ func ExampleBuild4DWithStats() {
 	fmt.Println(tr.Dim())
 	// Output: 4
 }
+
+func ExampleNewKDTreeFromDim_Insert() {
+	// Construct an empty 2D tree, insert a point, then query.
+	tr, _ := poindexter.NewKDTreeFromDim[string](2)
+	tr.Insert(poindexter.KDPoint[string]{ID: "A", Coords: []float64{0.1, 0.2}, Value: "alpha"})
+	p, _, ok := tr.Nearest([]float64{0, 0})
+	fmt.Printf("ok=%v id=%s dim=%d len=%d", ok, p.ID, tr.Dim(), tr.Len())
+	// Output: ok=true id=A dim=2 len=1
+}
+
+func ExampleKDTree_TiesBehavior() {
+	// Two points equidistant from the query; tie ordering is arbitrary,
+	// but distances are equal.
+	pts := []poindexter.KDPoint[int]{
+		{ID: "L", Coords: []float64{-1}},
+		{ID: "R", Coords: []float64{+1}},
+	}
+	tr, _ := poindexter.NewKDTree(pts)
+	ns, ds := tr.KNearest([]float64{0}, 2)
+	_ = ns // neighbor order is unspecified
+	fmt.Printf("equal=%.1f==%.1f? %v", ds[0], ds[1], ds[0] == ds[1])
+	// Output: equal=1.0==1.0? true
+}
+
+func ExampleKDTree_Radius_none() {
+	// Radius query that yields no matches.
+	pts := []poindexter.KDPoint[int]{
+		{ID: "a", Coords: []float64{10}},
+		{ID: "b", Coords: []float64{20}},
+	}
+	tr, _ := poindexter.NewKDTree(pts)
+	within, _ := tr.Radius([]float64{0}, 5)
+	fmt.Println(len(within))
+	// Output: 0
+}