英文:
Multiple-value in single-value context
问题
我目前正在尝试使用Go语言，并且遇到了上述的错误信息。请查看接口、float64的实现以及测试部分。
接口：
package interval
import (
"errors"
"fmt"
"math"
)
type Interval interface {
Intersect(Y Interval) (Interval, error) // 当为空时，返回错误'nil'
}
type floatInterval struct {
a, b float64
}
func (fi floatInterval) Intersect(Y Interval) (Interval, error) {
tmp := Y.(floatInterval)
a_new, b_new := math.Max(fi.a, tmp.a), math.Min(fi.b, tmp.b)
result := floatInterval{a_new, b_new}
if result.Length() == 0 {
return result, errors.New("空区间")
} else {
return result, nil
}
}
测试部分：
func intersect_test(t *testing.T, c testTuple) {
got, _ := c.iv1.Intersect(c.iv2).(floatInterval)
if (c.intersectWant.a != got.a) || (c.intersectWant.b != got.b) {
t.Errorf("期望值: [%f, %f] \t 实际值: [%f, %f]", c.intersectWant.a, c.intersectWant.b, got.a, got.b)
}
}
错误发生在测试函数的第二行。我知道Intersect函数返回两个值：区间和一个错误值。但是由于我使用了got, _ := c.iv1.Intersect(c.iv2).(floatInterval)来同时赋值给两个变量，我以为这样是安全的。顺便说一下，我也尝试过got, err := ...。这是因为我使用了.(floatInterval)进行类型转换吗？
英文:
I'm currently trying out Go and am stuck with the aforementioned error message. Have a look at the interface, its implementation for float64 and the test.
Interface:
package interval
import (
"errors"
"fmt"
"math"
)
type Interval interface {
Intersect(Y Interval) (Interval, error) // Intersection of X and Y, error 'nil' when empty
}
type floatInterval struct {
a, b float64
}
func (fi floatInterval) Intersect(Y Interval) (Interval, error) {
tmp := Y.(floatInterval)
a_new, b_new := math.Max(fi.a, tmp.a), math.Min(fi.b, tmp.b)
result := floatInterval{a_new, b_new}
if result.Length() == 0 {
return result, errors.New("Empty interval")
} else {
return result, nil
}
}
Test:
func intersect_test(t *testing.T, c testTuple) {
got, _ := c.iv1.Intersect(c.iv2).(floatInterval)
if (c.intersectWant.a != got.a) || (c.intersectWant.b != got.b) {
t.Errorf("Expected: [%f, %f] \t Got: [%f, %f]", c.intersectWant.a, c.intersectWant.b, got.a, got.b)
}
}
The error occurs in the second line of the test function. I am aware that intersect returns two values: The interval and an error value. But since I am assigning both with got, _ := c.iv1.Intersect(c.iv2).(floatInterval) I thought I'm on the safe side. I also tried got, err := ... by the way. Is that due to the type conversion I'm doing with .(floatInterval) ?
答案1
得分: 7
这是因为类型断言只接受单个值。
请改为以下方式：
gotInterval, _ := c.iv1.Intersect(c.iv2)
got := gotInterval.(floatInterval)
英文:
It's because of the type assertion, which takes only a single value.
Do this instead:
gotInterval, _ := c.iv1.Intersect(c.iv2)
got := gotInterval.(floatInterval)
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