Source file src/go/types/example_test.go

     1  // Copyright 2015 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  // Only run where builders (build.golang.org) have
     6  // access to compiled packages for import.
     7  //
     8  //go:build !arm && !arm64
     9  
    10  package types_test
    11  
    12  // This file shows examples of basic usage of the go/types API.
    13  //
    14  // To locate a Go package, use (*go/build.Context).Import.
    15  // To load, parse, and type-check a complete Go program
    16  // from source, use golang.org/x/tools/go/loader.
    17  
    18  import (
    19  	"bytes"
    20  	"fmt"
    21  	"go/ast"
    22  	"go/format"
    23  	"go/importer"
    24  	"go/parser"
    25  	"go/token"
    26  	"go/types"
    27  	"log"
    28  	"regexp"
    29  	"sort"
    30  	"strings"
    31  )
    32  
    33  // ExampleScope prints the tree of Scopes of a package created from a
    34  // set of parsed files.
    35  func ExampleScope() {
    36  	// Parse the source files for a package.
    37  	fset := token.NewFileSet()
    38  	var files []*ast.File
    39  	for _, file := range []struct{ name, input string }{
    40  		{"main.go", `
    41  package main
    42  import "fmt"
    43  func main() {
    44  	freezing := FToC(-18)
    45  	fmt.Println(freezing, Boiling) }
    46  `},
    47  		{"celsius.go", `
    48  package main
    49  import "fmt"
    50  type Celsius float64
    51  func (c Celsius) String() string { return fmt.Sprintf("%g°C", c) }
    52  func FToC(f float64) Celsius { return Celsius(f - 32 / 9 * 5) }
    53  const Boiling Celsius = 100
    54  func Unused() { {}; {{ var x int; _ = x }} } // make sure empty block scopes get printed
    55  `},
    56  	} {
    57  		f, err := parser.ParseFile(fset, file.name, file.input, 0)
    58  		if err != nil {
    59  			log.Fatal(err)
    60  		}
    61  		files = append(files, f)
    62  	}
    63  
    64  	// Type-check a package consisting of these files.
    65  	// Type information for the imported "fmt" package
    66  	// comes from $GOROOT/pkg/$GOOS_$GOOARCH/fmt.a.
    67  	conf := types.Config{Importer: importer.Default()}
    68  	pkg, err := conf.Check("temperature", fset, files, nil)
    69  	if err != nil {
    70  		log.Fatal(err)
    71  	}
    72  
    73  	// Print the tree of scopes.
    74  	// For determinism, we redact addresses.
    75  	var buf bytes.Buffer
    76  	pkg.Scope().WriteTo(&buf, 0, true)
    77  	rx := regexp.MustCompile(` 0x[a-fA-F0-9]*`)
    78  	fmt.Println(rx.ReplaceAllString(buf.String(), ""))
    79  
    80  	// Output:
    81  	// package "temperature" scope {
    82  	// .  const temperature.Boiling temperature.Celsius
    83  	// .  type temperature.Celsius float64
    84  	// .  func temperature.FToC(f float64) temperature.Celsius
    85  	// .  func temperature.Unused()
    86  	// .  func temperature.main()
    87  	// .  main.go scope {
    88  	// .  .  package fmt
    89  	// .  .  function scope {
    90  	// .  .  .  var freezing temperature.Celsius
    91  	// .  .  }
    92  	// .  }
    93  	// .  celsius.go scope {
    94  	// .  .  package fmt
    95  	// .  .  function scope {
    96  	// .  .  .  var c temperature.Celsius
    97  	// .  .  }
    98  	// .  .  function scope {
    99  	// .  .  .  var f float64
   100  	// .  .  }
   101  	// .  .  function scope {
   102  	// .  .  .  block scope {
   103  	// .  .  .  }
   104  	// .  .  .  block scope {
   105  	// .  .  .  .  block scope {
   106  	// .  .  .  .  .  var x int
   107  	// .  .  .  .  }
   108  	// .  .  .  }
   109  	// .  .  }
   110  	// .  }
   111  	// }
   112  }
   113  
   114  // ExampleMethodSet prints the method sets of various types.
   115  func ExampleMethodSet() {
   116  	// Parse a single source file.
   117  	const input = `
   118  package temperature
   119  import "fmt"
   120  type Celsius float64
   121  func (c Celsius) String() string  { return fmt.Sprintf("%g°C", c) }
   122  func (c *Celsius) SetF(f float64) { *c = Celsius(f - 32 / 9 * 5) }
   123  
   124  type S struct { I; m int }
   125  type I interface { m() byte }
   126  `
   127  	fset := token.NewFileSet()
   128  	f, err := parser.ParseFile(fset, "celsius.go", input, 0)
   129  	if err != nil {
   130  		log.Fatal(err)
   131  	}
   132  
   133  	// Type-check a package consisting of this file.
   134  	// Type information for the imported packages
   135  	// comes from $GOROOT/pkg/$GOOS_$GOOARCH/fmt.a.
   136  	conf := types.Config{Importer: importer.Default()}
   137  	pkg, err := conf.Check("temperature", fset, []*ast.File{f}, nil)
   138  	if err != nil {
   139  		log.Fatal(err)
   140  	}
   141  
   142  	// Print the method sets of Celsius and *Celsius.
   143  	celsius := pkg.Scope().Lookup("Celsius").Type()
   144  	for _, t := range []types.Type{celsius, types.NewPointer(celsius)} {
   145  		fmt.Printf("Method set of %s:\n", t)
   146  		mset := types.NewMethodSet(t)
   147  		for i := 0; i < mset.Len(); i++ {
   148  			fmt.Println(mset.At(i))
   149  		}
   150  		fmt.Println()
   151  	}
   152  
   153  	// Print the method set of S.
   154  	styp := pkg.Scope().Lookup("S").Type()
   155  	fmt.Printf("Method set of %s:\n", styp)
   156  	fmt.Println(types.NewMethodSet(styp))
   157  
   158  	// Output:
   159  	// Method set of temperature.Celsius:
   160  	// method (temperature.Celsius) String() string
   161  	//
   162  	// Method set of *temperature.Celsius:
   163  	// method (*temperature.Celsius) SetF(f float64)
   164  	// method (*temperature.Celsius) String() string
   165  	//
   166  	// Method set of temperature.S:
   167  	// MethodSet {}
   168  }
   169  
   170  // ExampleInfo prints various facts recorded by the type checker in a
   171  // types.Info struct: definitions of and references to each named object,
   172  // and the type, value, and mode of every expression in the package.
   173  func ExampleInfo() {
   174  	// Parse a single source file.
   175  	const input = `
   176  package fib
   177  
   178  type S string
   179  
   180  var a, b, c = len(b), S(c), "hello"
   181  
   182  func fib(x int) int {
   183  	if x < 2 {
   184  		return x
   185  	}
   186  	return fib(x-1) - fib(x-2)
   187  }`
   188  	fset := token.NewFileSet()
   189  	f, err := parser.ParseFile(fset, "fib.go", input, 0)
   190  	if err != nil {
   191  		log.Fatal(err)
   192  	}
   193  
   194  	// Type-check the package.
   195  	// We create an empty map for each kind of input
   196  	// we're interested in, and Check populates them.
   197  	info := types.Info{
   198  		Types: make(map[ast.Expr]types.TypeAndValue),
   199  		Defs:  make(map[*ast.Ident]types.Object),
   200  		Uses:  make(map[*ast.Ident]types.Object),
   201  	}
   202  	var conf types.Config
   203  	pkg, err := conf.Check("fib", fset, []*ast.File{f}, &info)
   204  	if err != nil {
   205  		log.Fatal(err)
   206  	}
   207  
   208  	// Print package-level variables in initialization order.
   209  	fmt.Printf("InitOrder: %v\n\n", info.InitOrder)
   210  
   211  	// For each named object, print the line and
   212  	// column of its definition and each of its uses.
   213  	fmt.Println("Defs and Uses of each named object:")
   214  	usesByObj := make(map[types.Object][]string)
   215  	for id, obj := range info.Uses {
   216  		posn := fset.Position(id.Pos())
   217  		lineCol := fmt.Sprintf("%d:%d", posn.Line, posn.Column)
   218  		usesByObj[obj] = append(usesByObj[obj], lineCol)
   219  	}
   220  	var items []string
   221  	for obj, uses := range usesByObj {
   222  		sort.Strings(uses)
   223  		item := fmt.Sprintf("%s:\n  defined at %s\n  used at %s",
   224  			types.ObjectString(obj, types.RelativeTo(pkg)),
   225  			fset.Position(obj.Pos()),
   226  			strings.Join(uses, ", "))
   227  		items = append(items, item)
   228  	}
   229  	sort.Strings(items) // sort by line:col, in effect
   230  	fmt.Println(strings.Join(items, "\n"))
   231  	fmt.Println()
   232  
   233  	fmt.Println("Types and Values of each expression:")
   234  	items = nil
   235  	for expr, tv := range info.Types {
   236  		var buf bytes.Buffer
   237  		posn := fset.Position(expr.Pos())
   238  		tvstr := tv.Type.String()
   239  		if tv.Value != nil {
   240  			tvstr += " = " + tv.Value.String()
   241  		}
   242  		// line:col | expr | mode : type = value
   243  		fmt.Fprintf(&buf, "%2d:%2d | %-19s | %-7s : %s",
   244  			posn.Line, posn.Column, exprString(fset, expr),
   245  			mode(tv), tvstr)
   246  		items = append(items, buf.String())
   247  	}
   248  	sort.Strings(items)
   249  	fmt.Println(strings.Join(items, "\n"))
   250  
   251  	// Output:
   252  	// InitOrder: [c = "hello" b = S(c) a = len(b)]
   253  	//
   254  	// Defs and Uses of each named object:
   255  	// builtin len:
   256  	//   defined at -
   257  	//   used at 6:15
   258  	// func fib(x int) int:
   259  	//   defined at fib.go:8:6
   260  	//   used at 12:20, 12:9
   261  	// type S string:
   262  	//   defined at fib.go:4:6
   263  	//   used at 6:23
   264  	// type int:
   265  	//   defined at -
   266  	//   used at 8:12, 8:17
   267  	// type string:
   268  	//   defined at -
   269  	//   used at 4:8
   270  	// var b S:
   271  	//   defined at fib.go:6:8
   272  	//   used at 6:19
   273  	// var c string:
   274  	//   defined at fib.go:6:11
   275  	//   used at 6:25
   276  	// var x int:
   277  	//   defined at fib.go:8:10
   278  	//   used at 10:10, 12:13, 12:24, 9:5
   279  	//
   280  	// Types and Values of each expression:
   281  	//  4: 8 | string              | type    : string
   282  	//  6:15 | len                 | builtin : func(fib.S) int
   283  	//  6:15 | len(b)              | value   : int
   284  	//  6:19 | b                   | var     : fib.S
   285  	//  6:23 | S                   | type    : fib.S
   286  	//  6:23 | S(c)                | value   : fib.S
   287  	//  6:25 | c                   | var     : string
   288  	//  6:29 | "hello"             | value   : string = "hello"
   289  	//  8:12 | int                 | type    : int
   290  	//  8:17 | int                 | type    : int
   291  	//  9: 5 | x                   | var     : int
   292  	//  9: 5 | x < 2               | value   : untyped bool
   293  	//  9: 9 | 2                   | value   : int = 2
   294  	// 10:10 | x                   | var     : int
   295  	// 12: 9 | fib                 | value   : func(x int) int
   296  	// 12: 9 | fib(x - 1)          | value   : int
   297  	// 12: 9 | fib(x-1) - fib(x-2) | value   : int
   298  	// 12:13 | x                   | var     : int
   299  	// 12:13 | x - 1               | value   : int
   300  	// 12:15 | 1                   | value   : int = 1
   301  	// 12:20 | fib                 | value   : func(x int) int
   302  	// 12:20 | fib(x - 2)          | value   : int
   303  	// 12:24 | x                   | var     : int
   304  	// 12:24 | x - 2               | value   : int
   305  	// 12:26 | 2                   | value   : int = 2
   306  }
   307  
   308  func mode(tv types.TypeAndValue) string {
   309  	switch {
   310  	case tv.IsVoid():
   311  		return "void"
   312  	case tv.IsType():
   313  		return "type"
   314  	case tv.IsBuiltin():
   315  		return "builtin"
   316  	case tv.IsNil():
   317  		return "nil"
   318  	case tv.Assignable():
   319  		if tv.Addressable() {
   320  			return "var"
   321  		}
   322  		return "mapindex"
   323  	case tv.IsValue():
   324  		return "value"
   325  	default:
   326  		return "unknown"
   327  	}
   328  }
   329  
   330  func exprString(fset *token.FileSet, expr ast.Expr) string {
   331  	var buf bytes.Buffer
   332  	format.Node(&buf, fset, expr)
   333  	return buf.String()
   334  }
   335  

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