为什么打包代码没有正文？ [重复]

I wondered coding style of go package when studying exporting packaging.

and found that the code of package in source(ex:"math", "fmt") has

function begins with a capital letter but no body.

I just follow this code but doesn't work.

Anyone who explain why??

func Abs(x float64) float64

func abs(x float64) float64 {
    switch {
    case x < 0:
        return -x
    case x == 0:
        return 0 // return correctly abs(-0)
    }
    return x
}

</div>

those functions are implemented in Assembler (https://golang.org/doc/asm) there are platform specific implementations for them: take a look at e.g.:

$GOROOT/src/math/abs_amd64.s

for

func Abs(x float64) float64