go - 类型开关不检测 float32

Question

package main

import "fmt"

func main() {
    printType(4.0)
}

func printType(i interface{}) {
    switch i := i.(type) {
    case float32:
        fmt.Println("This is a float type", i)
    }
}

出于某种原因，此代码未将 4.0 值检测为 float32，但将其检测为 float64 - 这是为什么呢？我在 win x64 机器上运行它。

Answer 1

For some reason this code does not detect 4.0 value as float32 but it detects it as float64 - why is that?

因为 float64 是 default type对于无类型浮点常量。相关部分强调:

An untyped constant has a default type which is the type to which the constant is implicitly converted in contexts where a typed value is required, for instance, in a short variable declaration such as i := 0 where there is no explicit type. The default type of an untyped constant is bool, rune, int, float64, complex128 or string respectively, depending on whether it is a boolean, rune, integer, floating-point, complex, or string constant.