On Sun, Mar 19, 2017 at 6:20 PM, Steven Hartland <ste...@multiplay.co.uk> wrote:
> Think the following section should explain the strange behaviour you're > seeing: > https://golang.org/ref/spec#Order_of_evaluation > > On 19/03/2017 22:59, Jan Mercl wrote: > > While trying to resolve a failing (C) test case[0] I encountered a (Go) > behavior I do not understand. This code[1] > > package main > > import ( > "fmt" > ) > > var ( > x = [1]int{2} > x2 = [1]int{2} > ) > > func foo() int { > x[0] |= 128 > return 1 > } > > func foo2() int { > x2[0] |= 128 > return 1 > } > > func main() { > x[0] |= foo() > fmt.Println(x[0]) > v := x2[0] | foo2() > fmt.Println(v) > } > > outputs: > > 3 > 131 > > It seems to me that the two numbers should be the same. (?) > > Logically yes, but due the implementation, along with "side effects" (undocumented?), it does. The "x[0]|=foo()" moves x[0] to a temporary area. It then invokes foo(). It then does the logical or from the "temporary area" (previous value of x[0]) with the return value from foo(), getting 3. v:= x2[0] | foo2() does compiles (on x86_64 at least) to : call foo2(); fetch the value of x2[0]; logically or it with the result from foo2(); store the result back into x2[0]. WHY does it generate the code this way? I have only the vaguest idea. I'm not a compiler writer. And I can't seem to find the documentation on exactly how "|=" works. I'm also not an Intel x86_64 assembler programmer, but I can get a general understanding of what is going on. > > Thanks in advance to anyone enlightening me. > > [0]: https://github.com/gcc-mirror/gcc/blob/ > 4107202e2b8f814f4c63a61b043cfb36a3798de3/gcc/testsuite/gcc. > c-torture/execute/pr58943.c > [1]: https://play.golang.org/p/fGibPFuejQ > > -- > > -j > > -- "Irrigation of the land with seawater desalinated by fusion power is ancient. It's called 'rain'." -- Michael McClary, in alt.fusion Maranatha! <>< John McKown -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
