go：整数除以浮点数的问题

Question

    fmt.Println(11 / (10.0 * 1))
    s := []byte("hello world")
    fmt.Println(len(s) / (10.0 * 1))

stdout:
1.1
1

两个的计算结果为什么不一致：都是int/float

Answer 1

这是因为第一个左侧类型为数值常量，会根据右侧运算值类型float类确定左侧类型，之后再运算，float/float=float，所以是1.1，而第二个len函数返回类型为确定的int，运算会按照左侧类型来执行，右侧被转换为int类型，因此就是int/int=int 值为1

// 如果左侧运算符类型确定，则右侧转为左侧类型再运算
var num1 int = 11
fmt.Println(num1 / 10)
fmt.Println(num1 / 10.0)

// 如果左侧类型不确定，则根据右侧类型推导左侧类型
fmt.Println(11 / 10)
fmt.Println(11 / 10.0)

自动类型转换参考 https://golang.org/ref/spec#C...

A constant value x can be converted to type T in any of these cases:

x is representable by a value of type T.
x is a floating-point constant, T is a floating-point type, and x is representable by a value of type T after rounding using IEEE 754 round-to-even rules, but with an IEEE -0.0 further rounded to an unsigned 0.0. The constant T(x) is the rounded value.
x is an integer constant and T is a string type. The same rule as for non-constant x applies in this case.