我应该将什么传递给 Crystal 中的以下方法？

Question

背景

我正在尝试使用 some Cairo bindings for Crystal，但我在语法以及如何调用下面的方法方面遇到了一些问题。它是这样实现的：

# Inside Module Cairo, class Surface

# ...

def write_to_png_stream(write_func : LibCairo::WriteFuncT, closure : Void*) : Status
   Status.new(LibCairo.surface_write_to_png_stream(@surface, write_func, closure).value)
end

# Inside Module LibCairo

# ...

enum StatusT
  SUCCESS = 0

  NO_MEMORY
  INVALID_RESTORE
  # ...
end

# ...

alias WriteFuncT = Void*, UInt8*, UInt32 -> StatusT

# ...

fun surface_write_to_png_stream = cairo_surface_write_to_png_stream(
  surface : PSurfaceT,
  write_func : WriteFuncT,
  closure : Void*
) : StatusT

问题

具体来说，我问的是如何调用 Cairo::Surface#write_to_png_stream 方法。我传递什么作为 write_func:LibCairo::WriteFuncT？我传递什么作为 closure: Void*?

我尝试了以下方法，但未能成功...

def my_write_func(a : Void*, b : UInt8*, c : UInt32) : Cairo::C::LibCairo::StatusT
   puts a
   puts b
   puts c

   Cairo::C::LibCairo::StatusT::SUCCESS
end

surface = Cairo::Surface.new Cairo::Format::ARGB32, 400, 300
ctx = Cairo::Context.new surface

ctx.set_source_rgba 1.0, 0.0, 1.0, 1.0
ctx.rectangle 0.0, 0.0, 400.0, 300.0
ctx.fill

# here, how do I call surface.write_to_png_stream passing my 'my_write_func'?
# a Proc doesn't seem to work.. ( ->my_write_func(Void*, UInt8*, UInt32) )

surface.finish

Answer 1

终于我让它工作了..或者至少我设法调用了它。

surface.write_to_png_stream ->my_write_func(Void*, UInt8*, UInt32), Pointer(Void).null

事实证明，正如我所怀疑的那样，它毕竟是一个 Proc，而且我也只需要一个空指针。为了将来参考，我有一个 issue at the repo 谈论这个方法的具体用法，但我想 syntax/semantics 问题在这里得到了回答。

我应该将什么传递给 Crystal 中的以下方法？

What am I supposed to pass to the following method in Crystal?

methods

syntax

semantics

crystal-lang

背景

问题