Add embed-directive example (#423)

* Add embed-directive example and rename embedding to struct-embedding

Signed-off-by: peterzhu1992 <peterzhu1992@gmail.com>

* Minor tweaks

Signed-off-by: peterzhu1992 <peterzhu1992@gmail.com>

* Add some improvements

Signed-off-by: peterzhu1992 <peterzhu1992@gmail.com>

* Add isDir() checks for measure.go and generate.go in tools

Signed-off-by: peterzhu1992 <peterzhu1992@gmail.com>

examples/embed-directive/embed-directive.go

@@ -0,0 +1,45 @@
+// `//go:embed` is a compiler directive that allows programs to include arbitrary
+// files/folders in the binary. Read more about go directive
+// [here](https://dave.cheney.net/2018/01/08/gos-hidden-pragmas).
+package main
+
+// If no exported identifiers is directly used from `embed` package,
+// you can add an underscore `_` before the package name. In this example, we simply
+// import it as we need to use the `embed.FS` type from the package.
+import (
+	//_ "embed"
+	"embed"
+)
+
+// Since one file is defined after the directive, the compiler will only include
+// this single file, followed by variable `single_file_string` to access as `string` type.
+//go:embed example_folder/single_file.txt
+var single_file_string string
+
+// Here is a similar example but include single file as `[]byte`.
+//go:embed example_folder/single_file.txt
+var single_file_byte []byte
+
+// We can also embed multiple files or even folders with wildcard.
+//go:embed example_folder/single_file.txt
+//go:embed example_folder/*.hash
+var folder_FS embed.FS
+
+func main() {
+
+	// Print out content of `example_single_file.txt` as `string`.
+	print(single_file_string)
+
+	// Now handle `[]byte`.
+	print(string(single_file_byte))
+
+	// Retrieve file(s) matching `*.hash` pattern by reading from variable `folder_FS` first,
+	// then print out.
+	hash_file1 := "example_folder/multi_file1.hash"
+	hash_file2 := "example_folder/multi_file2.hash"
+	hash_content1, _ := folder_FS.ReadFile(hash_file1)
+	hash_content2, _ := folder_FS.ReadFile(hash_file2)
+	print(string(hash_content1))
+	print(string(hash_content2))
+
+}

examples/embed-directive/embed-directive.hash

@@ -0,0 +1,2 @@
+e996755d889f01c99c353616fb2bdeac6c3be6e6
+-EXJc75EbN-

examples/embed-directive/embed-directive.sh

@@ -0,0 +1,14 @@
+# Use these commands to run the example.
+# (Note: due to limitation on go playground,
+# this example can only be run on your local machine.)
+$ mkdir -p example_folder
+$ echo "hello go" > example_folder/single_file.txt
+$ echo "123" > example_folder/multi_file1.hash
+$ echo "456" > example_folder/multi_file2.hash
+
+$ go run embed-directive.go
+hello go
+hello go
+123
+456
+

examples/embed-directive/example_folder/multi_file1.hash

@@ -0,0 +1 @@
+123

examples/embed-directive/example_folder/multi_file2.hash

@@ -0,0 +1 @@
+456

examples/embed-directive/example_folder/single_file.txt

@@ -0,0 +1 @@
+hello go