Reduce allocations when writing

Fix #494

If a row is full, don't bother allocating a new one, just return it.

Use the last populated row as a hint for the size of new rows.

Simplify checkSheet to remove row map

1 files changed, 27 insertions, 0 deletions

diff --git a/file_test.go b/file_test.go
new file mode 100644
index 0000000..6c30f4a
--- /dev/null
+++ b/file_test.go
@@ -0,0 +1,27 @@
+package excelize
+
+import (
+	"testing"
+)
+
+func BenchmarkWrite(b *testing.B) {
+	const s = "This is test data"
+	for i := 0; i < b.N; i++ {
+		f := NewFile()
+		for row := 1; row <= 10000; row++ {
+			for col := 1; col <= 20; col++ {
+				val, err := CoordinatesToCellName(col, row)
+				if err != nil {
+					panic(err)
+				}
+				f.SetCellDefault("Sheet1", val, s)
+			}
+		}
+		// Save xlsx file by the given path.
+		err := f.SaveAs("./test.xlsx")
+		if err != nil {
+			panic(err)
+		}
+	}
+
+}