Go could throw exception when type overflow, but not always.

int8(float64).go

package main

import (
    "fmt"
    "math"
)

func main() {
	fmt.Printf("%d\n", int8(math.Pow(2, 10))) // => 0
}

int8(float64)_2.go

package main

import (
    "fmt"
)

func main() {
    var f float64 = 129
    fmt.Printf("%d\n", int8(f)) // => -127
    fmt.Printf("%d\n", int8(float64(129))) // => constant 129 overflows int8
}