mirror of https://github.com/golang/go.git
go/types: add Example of API usage
Change-Id: I9d3253b80508d733053789d6cb9645e029bf52e4 Reviewed-on: https://go-review.googlesource.com/10927 Reviewed-by: Robert Griesemer <gri@golang.org>
This commit is contained in:
Alan Donovan
parent
5acba80aa2
commit
368f0ee6c4
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// Copyright 2015 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package types_test
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// This file shows examples of basic usage of the go/types API.
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//
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// To locate a Go package, use (*go/build.Context).Import.
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// To load, parse, and type-check a complete Go program
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// from source, use golang.org/x/tools/go/loader.
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import (
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"bytes"
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"fmt"
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"go/ast"
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"go/format"
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"go/importer"
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"go/parser"
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"go/token"
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"go/types"
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"log"
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"regexp"
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"sort"
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"strings"
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)
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// ExampleScope prints the tree of Scopes of a package created from a
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// set of parsed files.
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func ExampleScope() {
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// Parse the source files for a package.
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fset := token.NewFileSet()
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var files []*ast.File
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for _, file := range []struct{ name, input string }{
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{"main.go", `
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package main
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import "fmt"
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func main() {
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freezing := FToC(-18)
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fmt.Println(freezing, Boiling) }
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`},
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{"celsius.go", `
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package main
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import "fmt"
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type Celsius float64
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func (c Celsius) String() string { return fmt.Sprintf("%g°C", c) }
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func FToC(f float64) Celsius { return Celsius(f - 32 / 9 * 5) }
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const Boiling Celsius = 100
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`},
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} {
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f, err := parser.ParseFile(fset, file.name, file.input, 0)
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if err != nil {
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log.Fatal(err)
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}
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files = append(files, f)
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}
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// Type-check a package consisting of these files.
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// Type information for the imported "fmt" package
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// comes from $GOROOT/pkg/$GOOS_$GOOARCH/fmt.a.
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conf := types.Config{Importer: importer.Default()}
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pkg, err := conf.Check("temperature", fset, files, nil)
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if err != nil {
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log.Fatal(err)
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}
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// Print the tree of scopes.
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// For determinism, we redact addresses.
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var buf bytes.Buffer
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pkg.Scope().WriteTo(&buf, 0, true)
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rx := regexp.MustCompile(` 0x[a-fA-F0-9]*`)
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fmt.Println(rx.ReplaceAllString(buf.String(), ""))
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// Output:
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// package "temperature" scope {
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// . const temperature.Boiling temperature.Celsius
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// . type temperature.Celsius float64
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// . func temperature.FToC(f float64) temperature.Celsius
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// . func temperature.main()
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//
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// . main.go scope {
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// . . package fmt
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//
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// . . function scope {
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// . . . var freezing temperature.Celsius
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// . . }. }
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// . celsius.go scope {
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// . . package fmt
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//
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// . . function scope {
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// . . . var c temperature.Celsius
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// . . }
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// . . function scope {
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// . . . var f float64
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// . . }. }}
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}
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// ExampleMethodSet prints the method sets of various types.
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func ExampleMethodSet() {
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// Parse a single source file.
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const input = `
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package temperature
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import "fmt"
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type Celsius float64
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func (c Celsius) String() string { return fmt.Sprintf("%g°C", c) }
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func (c *Celsius) SetF(f float64) { *c = Celsius(f - 32 / 9 * 5) }
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`
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fset := token.NewFileSet()
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f, err := parser.ParseFile(fset, "celsius.go", input, 0)
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if err != nil {
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log.Fatal(err)
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}
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// Type-check a package consisting of this file.
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// Type information for the imported packages
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// comes from $GOROOT/pkg/$GOOS_$GOOARCH/fmt.a.
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conf := types.Config{Importer: importer.Default()}
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pkg, err := conf.Check("temperature", fset, []*ast.File{f}, nil)
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if err != nil {
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log.Fatal(err)
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}
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// Print the method sets of Celsius and *Celsius.
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celsius := pkg.Scope().Lookup("Celsius").Type()
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for _, t := range []types.Type{celsius, types.NewPointer(celsius)} {
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fmt.Printf("Method set of %s:\n", t)
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mset := types.NewMethodSet(t)
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for i := 0; i < mset.Len(); i++ {
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fmt.Println(mset.At(i))
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}
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fmt.Println()
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}
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// Output:
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// Method set of temperature.Celsius:
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// method (temperature.Celsius) String() string
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//
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// Method set of *temperature.Celsius:
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// method (*temperature.Celsius) SetF(f float64)
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// method (*temperature.Celsius) String() string
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}
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// ExampleInfo prints various facts recorded by the type checker in a
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// types.Info struct: definitions of and references to each named object,
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// and the type, value, and mode of every expression in the package.
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func ExampleInfo() {
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// Parse a single source file.
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const input = `
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package fib
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type S string
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var a, b, c = len(b), S(c), "hello"
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func fib(x int) int {
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if x < 2 {
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return x
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}
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return fib(x-1) - fib(x-2)
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}`
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fset := token.NewFileSet()
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f, err := parser.ParseFile(fset, "fib.go", input, 0)
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if err != nil {
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log.Fatal(err)
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}
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// Type-check the package.
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// We create an empty map for each kind of input
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// we're interested in, and Check populates them.
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info := types.Info{
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Types: make(map[ast.Expr]types.TypeAndValue),
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Defs: make(map[*ast.Ident]types.Object),
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Uses: make(map[*ast.Ident]types.Object),
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}
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var conf types.Config
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pkg, err := conf.Check("fib", fset, []*ast.File{f}, &info)
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if err != nil {
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log.Fatal(err)
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}
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// Print package-level variables in initialization order.
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fmt.Printf("InitOrder: %v\n\n", info.InitOrder)
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// For each named object, print the line and
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// column of its definition and each of its uses.
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fmt.Println("Defs and Uses of each named object:")
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usesByObj := make(map[types.Object][]string)
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for id, obj := range info.Uses {
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posn := fset.Position(id.Pos())
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lineCol := fmt.Sprintf("%d:%d", posn.Line, posn.Column)
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usesByObj[obj] = append(usesByObj[obj], lineCol)
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}
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var items []string
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for obj, uses := range usesByObj {
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sort.Strings(uses)
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item := fmt.Sprintf("%s:\n defined at %s\n used at %s",
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types.ObjectString(pkg, obj),
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fset.Position(obj.Pos()),
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strings.Join(uses, ", "))
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items = append(items, item)
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}
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sort.Strings(items) // sort by line:col, in effect
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fmt.Println(strings.Join(items, "\n"))
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fmt.Println()
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fmt.Println("Types and Values of each expression:")
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items = nil
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for expr, tv := range info.Types {
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var buf bytes.Buffer
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posn := fset.Position(expr.Pos())
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tvstr := tv.Type.String()
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if tv.Value != nil {
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tvstr += " = " + tv.Value.String()
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}
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// line:col | expr | mode : type = value
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fmt.Fprintf(&buf, "%2d:%2d | %-19s | %-7s : %s",
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posn.Line, posn.Column, exprString(fset, expr),
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mode(tv), tvstr)
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items = append(items, buf.String())
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}
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sort.Strings(items)
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fmt.Println(strings.Join(items, "\n"))
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// Output:
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// InitOrder: [c = "hello" b = S(c) a = len(b)]
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//
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// Defs and Uses of each named object:
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// builtin len:
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// defined at -
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// used at 6:15
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// func fib(x int) int:
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// defined at fib.go:8:6
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// used at 12:20, 12:9
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// type S string:
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// defined at fib.go:4:6
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// used at 6:23
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// type int int:
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// defined at -
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// used at 8:12, 8:17
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// type string string:
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// defined at -
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// used at 4:8
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// var b S:
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// defined at fib.go:6:8
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// used at 6:19
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// var c string:
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// defined at fib.go:6:11
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// used at 6:25
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// var x int:
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// defined at fib.go:8:10
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// used at 10:10, 12:13, 12:24, 9:5
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//
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// Types and Values of each expression:
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// 4: 8 | string | type : string
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// 6:15 | len | builtin : func(string) int
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// 6:15 | len(b) | value : int
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// 6:19 | b | var : fib.S
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// 6:23 | S | type : fib.S
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// 6:23 | S(c) | value : fib.S
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// 6:25 | c | var : string
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// 6:29 | "hello" | value : string = "hello"
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// 8:12 | int | type : int
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// 8:17 | int | type : int
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// 9: 5 | x | var : int
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// 9: 5 | x < 2 | value : untyped bool
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// 9: 9 | 2 | value : int = 2
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// 10:10 | x | var : int
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// 12: 9 | fib | value : func(x int) int
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// 12: 9 | fib(x - 1) | value : int
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// 12: 9 | fib(x-1) - fib(x-2) | value : int
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// 12:13 | x | var : int
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// 12:13 | x - 1 | value : int
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// 12:15 | 1 | value : int = 1
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// 12:20 | fib | value : func(x int) int
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// 12:20 | fib(x - 2) | value : int
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// 12:24 | x | var : int
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// 12:24 | x - 2 | value : int
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// 12:26 | 2 | value : int = 2
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}
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func mode(tv types.TypeAndValue) string {
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switch {
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case tv.IsVoid():
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return "void"
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case tv.IsType():
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return "type"
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case tv.IsBuiltin():
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return "builtin"
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case tv.IsNil():
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return "nil"
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case tv.Assignable():
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if tv.Addressable() {
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return "var"
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}
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return "mapindex"
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case tv.IsValue():
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return "value"
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default:
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return "unknown"
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}
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}
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func exprString(fset *token.FileSet, expr ast.Expr) string {
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var buf bytes.Buffer
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format.Node(&buf, fset, expr)
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return buf.String()
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}
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