Is it possible to include an external file as a string constant in go?

I always wished it was possible to do something like this in C++:

const std::string fragmentShader = "
#include "shader.frag"
";

Obviously that doesn't work, and there is no way to do it in C++. But it is possible in go? i.e.

const fragmentShader string = `
<insert contents of shader.frag at compile-time>
`

The motivation should be obvious!

Not really, but here are a couple options:

1. Just take the contents of the file and put them in your source code:

   const fragmentShaderFile = `contents of shader.frag`
   

2. You can embed assets with this tool: https://github.com/jteeuwen/go-bindata, but you'll have to re-embed the file anytime it's changed. (One could automate this as a git pre-commit hook though)

<s>This is not possible in pure Go.</s>¹ You could however write a program that reads a file and creates a Go file from it, such as this:

package main
import "flag"
import "os"
import "fmt"
import "bufio"
import "io"
var (
packageName = flag.String("p", "main", "package name")
outFile     = flag.String("o", "-", "output file. Defaults to stdout")
varName     = flag.String("v", "file", "variable name")
)
const (
header  = "package %s\n\nvar %s = [...]byte{\n"
trailer = "}\n"
)
func main() {
flag.Parse()
if len(flag.Args()) != 1 {
fmt.Fprintln(os.Stderr, "Please provide exactly one file name")
os.Exit(1)
}
var inF, outF *os.File
if *outFile == "-" {
outF = os.Stdout
} else {
var err error
outF, err = os.Create(*outFile)
if err != nil {
fmt.Fprintf(os.Stderr, "Cannot create %s: %v\n", *outFile, err)
os.Exit(1)
}
}
inF, err := os.Open(flag.Args()[0])
if err != nil {
fmt.Fprintf(os.Stderr, "Cannot open %s: %v\n", flag.Args()[0], err)
os.Exit(1)
}
in, out := bufio.NewReader(inF), bufio.NewWriter(outF)
fmt.Fprintf(out, header, *packageName, *varName)
buf := make([]byte, 16)
var n int
for n, err = io.ReadFull(in, buf); n > 0; n, err = io.ReadFull(in, buf) {
out.WriteRune('\t')
for i := 0; i < n-1; i++ {
fmt.Fprintf(out, "%#02x, ", buf[i])
}
fmt.Fprintf(out, "%#02x,\n", buf[n-1])
}
out.WriteString(trailer)
out.Flush()
if err != io.EOF {
fmt.Fprintf(os.Stderr, "An error occured while reading from %s: %v\n", flag.Args()[0], err)
os.Exit(1)
}
}

¹&emsp;This is now supported. You can use the embed mechanism as explained in my other answer.

These days, you should probably use the embed mechanism. For your use case, that would be like

import _ "embed"
//go:embed shader.frag
var fragmentShader string