英文:
Golang's type system behaviour - dividing an int by an implicit float
问题
最近我在尝试使用Go语言的类型系统时遇到了一个有趣（或者不是很有趣）的与浮点数相关的行为：
package main
import (
"fmt"
)
func main() {
doesntWork()
works()
}
func doesntWork() {
x := 1234
y := x / 100000.0
s := fmt.Sprintf("%.8f", y)
fmt.Printf("%s\n", s)
}
func works() {
x := 1234
y := float64(x) / 100000.0
s := fmt.Sprintf("%.8f", y)
fmt.Printf("%s\n", s)
}
我认为在上面的示例中，在doesntWork()函数中，当将int除以隐式的float时，Go语言不会自动假设为float32/64。这样理解正确吗？有人可以指导我查阅一些文档或规范，以了解Go语言在类似上述情况下的行为吗？
英文:
I was experimenting lately with golang's type system and encountered an interesting (or not) behaviour related to floats:
package main
import (
"fmt"
)
func main() {
doesntWork()
works()
}
func doesntWork() {
x := 1234
y := x / 100000.0
s := fmt.Sprintf("%.8f", y)
fmt.Printf("%s\n", s)
}
func works() {
x := 1234
y := float64(x) / 100000.0
s := fmt.Sprintf("%.8f", y)
fmt.Printf("%s\n", s)
}
I think that in the case presented in the example above, in procedure doesntWork(), golang does not automatically "assume" float32/64 when dividing an int by an implicit float? Is that correct? Could anyone point me towards some docs or specs where I could learn more about how golang behaves in situations like the one above?
答案1
得分: 6
这里的10000.0不是float64/32类型，而是一个数值常量。在这种情况下，Go语言会根据表达式中的x的类型来推断，并将常量100000.0截断为整数。
如果你将代码更新为：
func doesntWork() {
x := 1234
y := x / float64(100000.0)
s := fmt.Sprintf("%.8f", y)
fmt.Printf("%s\n", s)
}
它会报错，提示：
invalid operation: x / float64(100000) (mismatched types int and float64)
同样地，如果你将常量改为100000.111，其中truncate到整数将不再给出相同的值，它也会报错：
func doesntWork() {
x := 1234
y := x / 100000.1
s := fmt.Sprintf("%.8f", y)
fmt.Printf("%s\n", s)
}
它会报错，提示：
constant 100000 truncated to integer
英文:
Here 10000.0 is not float64/32 it is a numeric constant. Go will assume the type of x in this case for the expression and truncate the constant 100000.0 to integer
func doesntWork() {
x := 1234
y := x / 100000.0
s := fmt.Sprintf("%.8f", y)
fmt.Printf("%s\n", s)
}
If you update it to
func doesntWork() {
x := 1234
y := x / float64(100000.0)
s := fmt.Sprintf("%.8f", y)
fmt.Printf("%s\n", s)
}
it will error out saying
invalid operation: x / float64(100000) (mismatched types int and float64)
Similarly if you change the constant to 100000.111 where truncating to integer will no longer give the same value it will error out
func doesntWork() {
x := 1234
y := x / 100000.1
s := fmt.Sprintf("%.8f", y)
fmt.Printf("%s\n", s)
}
It will error out saying
constant 100000 truncated to integer
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