example_test.go

Documentation: go/constant

     1  // Copyright 2018 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  package constant_test
     6  
     7  import (
     8  	"fmt"
     9  	"go/constant"
    10  	"go/token"
    11  	"math"
    12  	"sort"
    13  )
    14  
    15  func Example_complexNumbers() {
    16  	// Create the complex number 2.3 + 5i.
    17  	ar := constant.MakeFloat64(2.3)
    18  	ai := constant.MakeImag(constant.MakeInt64(5))
    19  	a := constant.BinaryOp(ar, token.ADD, ai)
    20  
    21  	// Compute (2.3 + 5i) * 11.
    22  	b := constant.MakeUint64(11)
    23  	c := constant.BinaryOp(a, token.MUL, b)
    24  
    25  	// Convert c into a complex128.
    26  	Ar, exact := constant.Float64Val(constant.Real(c))
    27  	if !exact {
    28  		fmt.Printf("Could not represent real part %s exactly as float64\n", constant.Real(c))
    29  	}
    30  	Ai, exact := constant.Float64Val(constant.Imag(c))
    31  	if !exact {
    32  		fmt.Printf("Could not represent imaginary part %s as exactly as float64\n", constant.Imag(c))
    33  	}
    34  	C := complex(Ar, Ai)
    35  
    36  	fmt.Println("literal", 25.3+55i)
    37  	fmt.Println("go/constant", c)
    38  	fmt.Println("complex128", C)
    39  
    40  	// Output:
    41  	//
    42  	// Could not represent real part 25.3 exactly as float64
    43  	// literal (25.3+55i)
    44  	// go/constant (25.3 + 55i)
    45  	// complex128 (25.299999999999997+55i)
    46  }
    47  
    48  func ExampleBinaryOp() {
    49  	// 11 / 0.5
    50  	a := constant.MakeUint64(11)
    51  	b := constant.MakeFloat64(0.5)
    52  	c := constant.BinaryOp(a, token.QUO, b)
    53  	fmt.Println(c)
    54  
    55  	// Output: 22
    56  }
    57  
    58  func ExampleUnaryOp() {
    59  	vs := []constant.Value{
    60  		constant.MakeBool(true),
    61  		constant.MakeFloat64(2.7),
    62  		constant.MakeUint64(42),
    63  	}
    64  
    65  	for i, v := range vs {
    66  		switch v.Kind() {
    67  		case constant.Bool:
    68  			vs[i] = constant.UnaryOp(token.NOT, v, 0)
    69  
    70  		case constant.Float:
    71  			vs[i] = constant.UnaryOp(token.SUB, v, 0)
    72  
    73  		case constant.Int:
    74  			// Use 16-bit precision.
    75  			// This would be equivalent to ^uint16(v).
    76  			vs[i] = constant.UnaryOp(token.XOR, v, 16)
    77  		}
    78  	}
    79  
    80  	for _, v := range vs {
    81  		fmt.Println(v)
    82  	}
    83  
    84  	// Output:
    85  	//
    86  	// false
    87  	// -2.7
    88  	// 65493
    89  }
    90  
    91  func ExampleCompare() {
    92  	vs := []constant.Value{
    93  		constant.MakeString("Z"),
    94  		constant.MakeString("bacon"),
    95  		constant.MakeString("go"),
    96  		constant.MakeString("Frame"),
    97  		constant.MakeString("defer"),
    98  		constant.MakeFromLiteral(`"a"`, token.STRING, 0),
    99  	}
   100  
   101  	sort.Slice(vs, func(i, j int) bool {
   102  		// Equivalent to vs[i] <= vs[j].
   103  		return constant.Compare(vs[i], token.LEQ, vs[j])
   104  	})
   105  
   106  	for _, v := range vs {
   107  		fmt.Println(constant.StringVal(v))
   108  	}
   109  
   110  	// Output:
   111  	//
   112  	// Frame
   113  	// Z
   114  	// a
   115  	// bacon
   116  	// defer
   117  	// go
   118  }
   119  
   120  func ExampleSign() {
   121  	zero := constant.MakeInt64(0)
   122  	one := constant.MakeInt64(1)
   123  	negOne := constant.MakeInt64(-1)
   124  
   125  	mkComplex := func(a, b constant.Value) constant.Value {
   126  		b = constant.MakeImag(b)
   127  		return constant.BinaryOp(a, token.ADD, b)
   128  	}
   129  
   130  	vs := []constant.Value{
   131  		negOne,
   132  		mkComplex(zero, negOne),
   133  		mkComplex(one, negOne),
   134  		mkComplex(negOne, one),
   135  		mkComplex(negOne, negOne),
   136  		zero,
   137  		mkComplex(zero, zero),
   138  		one,
   139  		mkComplex(zero, one),
   140  		mkComplex(one, one),
   141  	}
   142  
   143  	for _, v := range vs {
   144  		fmt.Printf("% d %s\n", constant.Sign(v), v)
   145  	}
   146  
   147  	// Output:
   148  	//
   149  	// -1 -1
   150  	// -1 (0 + -1i)
   151  	// -1 (1 + -1i)
   152  	// -1 (-1 + 1i)
   153  	// -1 (-1 + -1i)
   154  	//  0 0
   155  	//  0 (0 + 0i)
   156  	//  1 1
   157  	//  1 (0 + 1i)
   158  	//  1 (1 + 1i)
   159  }
   160  
   161  func ExampleVal() {
   162  	maxint := constant.MakeInt64(math.MaxInt64)
   163  	fmt.Printf("%v\n", constant.Val(maxint))
   164  
   165  	e := constant.MakeFloat64(math.E)
   166  	fmt.Printf("%v\n", constant.Val(e))
   167  
   168  	b := constant.MakeBool(true)
   169  	fmt.Printf("%v\n", constant.Val(b))
   170  
   171  	b = constant.Make(false)
   172  	fmt.Printf("%v\n", constant.Val(b))
   173  
   174  	// Output:
   175  	//
   176  	// 9223372036854775807
   177  	// 6121026514868073/2251799813685248
   178  	// true
   179  	// false
   180  }
   181
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