errorerrorerror
errorerror
Newerror
errorerrors
NewerrorNew
// Package errors implements functions to manipulate errors.
  package errors

  // New returns an error that formats as the given text.
  func New(text string) error {
      return &errorString{text}
  }

  // errorString is a trivial implementation of error.
  type errorString struct {
      s string
  }

  func (e *errorString) Error() string {
      return e.s
  }
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errorStringserrorErrorerrorString
NewerrorStringerror
Newerror
error
package main

import (
    "errors"
    "fmt"
    "math"
)

func circleArea(radius float64) (float64, error) {
    if radius < 0 {
        return 0, errors.New("Area calculation failed, radius is less than zero")
    }
    return math.Pi * radius * radius, nil
}

func main() {
    radius := -20.0
    area, err := circleArea(radius)
    if err != nil {
        fmt.Println(err)
        return
    }
    fmt.Printf("Area of circle %0.2f", area)
}
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errornilerror
errornilnil

在这个程序中，半径小于零，因此它将打印，

Area calculation failed, radius is less than zero
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Errorferror
fmtErrorferror
Errorf
package main

import (
    "fmt"
    "math"
)

func circleArea(radius float64) (float64, error) {
    if radius < 0 {
        return 0, fmt.Errorf("Area calculation failed, radius %0.2f is less than zero", radius)
    }
    return math.Pi * radius * radius, nil
}

func main() {
    radius := -20.0
    area, err := circleArea(radius)
    if err != nil {
        fmt.Println(err)
        return
    }
    fmt.Printf("Area of circle %0.2f", area)
}
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Errorf
Area calculation failed, radius -20.00 is less than zero
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error
errorArea calculation failed, radius -20.00 is less than zero
errradiuserror
errorErrorareaError
type areaError struct {
    err    string
    radius float64
}
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radiuserrorerr
error
func (e *areaError) Error() string {
    return fmt.Sprintf("radius %0.2f: %s", e.radius, e.err)
}
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* areaErrorErrorradiuserr
maincircleArea
package main

import (
    "fmt"
    "math"
)

type areaError struct {
    err    string
    radius float64
}

func (e *areaError) Error() string {
    return fmt.Sprintf("radius %0.2f: %s", e.radius, e.err)
}

func circleArea(radius float64) (float64, error) {
    if radius < 0 {
        return 0, &areaError{"radius is negative", radius}
    }
    return math.Pi * radius * radius, nil
}

func main() {
    radius := -20.0
    area, err := circleArea(radius)
    if err != nil {
        if err, ok := err.(*areaError); ok {
            fmt.Printf("Radius %0.2f is less than zero", err.radius)
            return
        }
        fmt.Println(err)
        return
    }
    fmt.Printf("Area of rectangle1 %0.2f", area)
}
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circleAreaareaErrorareaErrorerrorerror
nil
main
errnilerr* areaError* areaError类型err.radiuserrorradius

输出，

Radius -20.00 is less than zero
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error
error

在本节中，我们将编写一个计算矩形区域的程序。如果长度或宽度小于 0，该程序将打印错误。

error
type areaError struct {
    err    string //error description
    length float64 //length which caused the error
    width  float64 //width which caused the error
}
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errlengthwidth
errorerror
func (e *areaError) Error() string {
    return e.err
}

func (e *areaError) lengthNegative() bool {
    return e.length < 0
}

func (e *areaError) widthNegative() bool {
    return e.width < 0
}
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Errore.errlengthlengthNegativetruewidthwidthNegativetrueerror

下一步是实现面积计算功能。

func rectArea(length, width float64) (float64, error) {
    err := ""
    if length < 0 {
        err += "length is less than zero"
    }
    if width < 0 {
        if err == "" {
            err = "width is less than zero"
        } else {
            err += ", width is less than zero"
        }
    }
    if err != "" {
        return 0, &areaError{err, length, width}
    }
    return length * width, nil
}
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rectAreaerrornilmain
func main() {
    length, width := -5.0, -9.0
    area, err := rectArea(length, width)
    if err != nil {
        if err, ok := err.(*areaError); ok {
            if err.lengthNegative() {
                fmt.Printf("error: length %0.2f is less than zero\n", err.length)

            }
            if err.widthNegative() {
                fmt.Printf("error: width %0.2f is less than zero\n", err.width)

            }
            return
        }
        fmt.Println(err)
        return
    }
    fmt.Println("area of rect", area)
}
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mainerrnilnil* areaErrorlengthNegativewidthNegativeerror

如果没有错误，将打印矩形面积。

最后贴出完整的程序供参考。

package main

import "fmt"

type areaError struct {
    err    string  //error description
    length float64 //length which caused the error
    width  float64 //width which caused the error
}

func (e *areaError) Error() string {
    return e.err
}

func (e *areaError) lengthNegative() bool {
    return e.length < 0
}

func (e *areaError) widthNegative() bool {
    return e.width < 0
}

func rectArea(length, width float64) (float64, error) {
    err := ""
    if length < 0 {
        err += "length is less than zero"
    }
    if width < 0 {
        if err == "" {
            err = "width is less than zero"
        } else {
            err += ", width is less than zero"
        }
    }
    if err != "" {
        return 0, &areaError{err, length, width}
    }
    return length * width, nil
}

func main() {
    length, width := -5.0, -9.0
    area, err := rectArea(length, width)
    if err != nil {
        if err, ok := err.(*areaError); ok {
            if err.lengthNegative() {
                fmt.Printf("error: length %0.2f is less than zero\n", err.length)

            }
            if err.widthNegative() {
                fmt.Printf("error: width %0.2f is less than zero\n", err.width)

            }
            return
        }
    }
    fmt.Println("area of rect", area)
}
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error: length -5.00 is less than zero
error: width -9.00 is less than zero
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error
error