Merge pull request #543 from devlights/add-three-index-slice-example

Author: devlights

examples/basic/slices/examples.go

@@ -28,4 +28,5 @@ func (r *register) Regist(m mapping.ExampleMapping) {
 	m["slice_remove_all_elements"] = RemoveAllElements
 	m["slice_keep_allocated_memory"] = KeepAllocatedMemory
 	m["slice_nil_append"] = NilAppend
+	m["slice_three_index"] = ThreeIndex
 }

examples/basic/slices/slice_three_index.go

@@ -0,0 +1,42 @@
+package slices
+
+import "github.com/devlights/gomy/output"
+
+// ThreeIndex は、スライスにて３つのインデックス指定をした場合のサンプルです.
+//
+// Three-index slices の仕様は、 Go 1.2 にて導入されたもの。
+// 3つ目のインデックス指定は、capacity の量を意図的に調整するためにある。
+//
+// REFERENCES
+//   - https://stackoverflow.com/questions/27938177/golang-slice-slicing-a-slice-with-sliceabc
+//   - https://stackoverflow.com/questions/12768744/re-slicing-slices-in-golang/18911267#18911267
+//   - https://tip.golang.org/doc/go1.2#three_index
+//   - https://go.dev/ref/spec#Slice_expressions
+func ThreeIndex() error {
+	var (
+		s = []string{
+			"golang",
+			"dotnet",
+			"java",
+			"python",
+			"ruby",
+		}
+		s2 = s[1:3]
+		s3 = s[1:3:4]
+	)
+
+	output.Stdoutf("[s      ]", "slice=%v\tlen=%v\tcap=%v\n", s, len(s), cap(s))
+	output.StdoutHr()
+
+	output.Stdoutl("[len(s2)]", "len => high(2nd) - low(1st) => 3      - 1 => 2")
+	output.Stdoutl("[cap(s2)]", "cap => max(3rd)  - low(1st) => len(s) - 1 => 5 - 1 => 4")
+	output.Stdoutf("[s2     ]", "slice=%v\tlen=%v\tcap=%v\n", s2, len(s2), cap(s2))
+
+	output.StdoutHr()
+
+	output.Stdoutl("[len(s3)]", "len => high(2nd) - low(1st) => 3 - 1 => 2")
+	output.Stdoutl("[cap(s3)]", "cap => max(3rd)  - low(1st) => 4 - 1 => 3")
+	output.Stdoutf("[s3     ]", "slice=%v\tlen=%v\tcap=%v\n", s3, len(s3), cap(s3))
+
+	return nil
+}