On Tuesday, September 10, 2019 at 3:18:47 PM UTC-4, burak serdar wrote:
>
> On Tue, Sep 10, 2019 at 1:13 PM Tong Sun <sunto...@gmail.com <javascript:>>
> wrote:
> >
> > I'm experiencing a weird problem with my program and finally nail it
> down to what exactly went wrong, so that I can write a minimum program to
> duplicate it. See the following program:
> >
> > package main
> >
> >
> > import (
> > "fmt"
> > )
> >
> >
> > type Vertex struct {
> > X int
> > Y int
> > }
> >
> >
> > func main() {
> > vs := []Vertex{
> > Vertex{1, 2}, // has type Vertex
> > Vertex{X: 3}, // Y:0 is implicit
> > Vertex{}, // X:0 and Y:0
> > }
> >
> >
> > fmt.Printf("Vertex Slice %+v\n", vs)
> > var vp *Vertex = nil
> > for _, v := range vs {
> > if v.X == 3 {
> > vp = &v
> > }
> > }
> > fmt.Printf("Found: %+v\n", vp)
> > }
> >
> >
> > https://play.golang.org/p/R645C5plojx
> >
> > I was expecting that the found Vertex is "v.X == 3", however the result
> is not.
>
> Because you're keeping a pointer to the loop variable. v continues
> changing after you store the address of it, so you get the latest
> value of v. Instead, save a copy of v, or break the loop as soon as
> what you're looking for is found:
>
I can't break the loop immediately as my not-minimized real program use a
double loop to find the *closest *item. That's the reason I using the
pointer to track my finding...
if v.x==3 {
> t:=v
> vp=&t
> }
>
OK. will do that. thx
>
> > - what exactly is causing the problem?
> > - how to fix it so that I got what I was looking for?
> >
> > Again, the snip is at
> > https://play.golang.org/p/R645C5plojx
> >
> > Thanks
> >
> > --
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>
>
>
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