Question

如果你看一看这里的图像包: 你们可以看到,每个图像的奥帕克(Opaque)的采用情况相同,仅在与钢材不同的逻辑上有所不同。

是否有理由这样做? 任何一般性解决办法是否效率不高? 它是否只是监督? 是否对使多变性[即通用]办法难以采用的类型系统存在某种限制(我看不到一)。

[编辑] 我所想的那种解决办法(从 Java的角度来看,不需要通用的)是:


type ColorPredicate func(c image.Color) bool;

func AllPixels (p *image.Image, q ColorPredicate) bool {
  var r = p.Bounds()
  if r.Empty() {
    return true
  }
  for y := r.Min.Y; y < r.Max.Y; y++ {
    for x := r.Min.X; x < r.Max.X; x++ {
      if ! q(p.At(x,y)) {
        return false
      }
    }
  }
  return true
}

but I am having trouble getting that to compile (still very new to Go - it will compile with an image, but not with an image pointer!).

这难道太难以选择吗? (青年需要发挥排他性的作用,但会把任何类型的检查从 lo中删除?) 而且,我现在想到的是,我过去曾用过“遗传”一词,我只用笼统(ha)的方式使用。

Answer 1

There is a limitation to the type system which prevents a general solution (or at least makes it very inefficient).

例如,阿根廷移民总局的机构。 Opaque和NRGBA。 Opaque是一样的,因此,你认为,可以将它们纳入具有类似签名的第三个职能:

func opaque(pix []Color, stride int, rect Rectangle) bool

请将此职能称为:

func (p *RGBA) Opaque() bool {
    return opaque([]Color(p.Pix), p.Stride, p.Rect)
}

But you can t. p.Pix can t be converted to []Color because those types have different in-memory representations and the spec forbids it. We could allocate a new slice, convert each individual element of p.Pix, and pass that, but that would be very inefficient.

认为阿根廷移民总局和阿根廷移民总局拥有同样的结构。或许我们可以将这两种功能排除在外,因为皮尔斯的内层代表完全相同:

func opaque(pix []RGBAColor, stride int, rect Rectangle) bool

func (p *NRGBA) Opaque() bool {
    return opaque([]RGBAColor(p.Pix), p.Stride, p.Rect)
}

Alas, again this isn t allowed. This seems to be more of a spec/language issue than a technical one. I m sure this has come up on the mailing list before, but I can t find a good discussion of it.

这似乎像一个通商会聚居的领域,但是在戈尔没有解决非专利问题。

Answer 2

Why does Go not have generic types?

Generics may well be added at some point. We don t feel an urgency for them, although we understand some programmers do.

Generics are convenient but they come at a cost in complexity in the type system and run-time. We haven t yet found a design that gives value proportionate to the complexity, although we continue to think about it. Meanwhile, Go s built-in maps and slices, plus the ability to use the empty interface to construct containers (with explicit unboxing) mean in many cases it is possible to write code that does what generics would enable, if less smoothly.

这仍然是一个开放的问题。

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