Info in Go
ExampleInfo prints various facts recorded by the type checker in a types.Info struct: definitions of and references to each named object, and the type, value, and mode of every expression in the package.
package main
import (
"bytes"
"fmt"
"go/ast"
"go/parser"
"go/token"
"go/types"
"log"
"sort"
"strings"
)
func main() {
// Parse a single source file.
const input = `
package fib
type S string
var a, b, c = len(b), S(c), "hello"
func fib(x int) int {
if x < 2 {
return x
}
return fib(x-1) - fib(x-2)
}`
fset := token.NewFileSet()
f, err := parser.ParseFile(fset, "fib.go", input, 0)
if err != nil {
log.Fatal(err)
}
// Type-check the package.
// We create an empty map for each kind of input
// we're interested in, and Check populates them.
info := types.Info{
Types: make(map[ast.Expr]types.TypeAndValue),
Defs: make(map[*ast.Ident]types.Object),
Uses: make(map[*ast.Ident]types.Object),
}
var conf types.Config
pkg, err := conf.Check("fib", fset, []*ast.File{f}, &info)
if err != nil {
log.Fatal(err)
}
// Print package-level variables in initialization order.
fmt.Printf("InitOrder: %v\n\n", info.InitOrder)
// For each named object, print the line and
// column of its definition and each of its uses.
fmt.Println("Defs and Uses of each named object:")
usesByObj := make(map[types.Object][]string)
for id, obj := range info.Uses {
posn := fset.Position(id.Pos())
lineCol := fmt.Sprintf("%d:%d", posn.Line, posn.Column)
usesByObj[obj] = append(usesByObj[obj], lineCol)
}
var items []string
for obj, uses := range usesByObj {
sort.Strings(uses)
item := fmt.Sprintf("%s:\n defined at %s\n used at %s",
types.ObjectString(obj, types.RelativeTo(pkg)),
fset.Position(obj.Pos()),
strings.Join(uses, ", "))
items = append(items, item)
}
sort.Strings(items) // sort by line:col, in effect
fmt.Println(strings.Join(items, "\n"))
fmt.Println()
fmt.Println("Types and Values of each expression:")
items = nil
for expr, tv := range info.Types {
var buf bytes.Buffer
posn := fset.Position(expr.Pos())
tvstr := tv.Type.String()
if tv.Value != nil {
tvstr += " = " + tv.Value.String()
}
// line:col | expr | mode : type = value
fmt.Fprintf(&buf, "%2d:%2d | %-19s | %-7s : %s",
posn.Line, posn.Column, exprString(fset, expr),
mode(tv), tvstr)
items = append(items, buf.String())
}
sort.Strings(items)
fmt.Println(strings.Join(items, "\n"))
}