考虑以下两个FFI结构:
class A < FFI::Struct
layout :data, :int
end
class B < FFI::Struct
layout :nested, A
end
实例化它们:
a = A.new
b = B.new
现在,当我尝试将a
分配给b.nested
时,如下所示:
b[:nested] = a
我得到以下错误:
ArgumentError: put not supported for FFI::StructByValue
如果嵌套结构是"按值嵌套"的,也就是说它不是指针,那么FFI似乎不允许使用[]语法进行赋值。如果是,如何将a
分配给b.nested
?
当你使用FFI嵌套时,它可以像这样工作:
b = B.new
b[:nested][:data] = 42
b[:nested][:data] #=> 42
外国金融机构"b"对象创建了自己的"a"对象;你不需要创建自己的。
看起来你想做的是创建自己的"a"对象,然后存储它:
a = A.new
b = B.new
b[:nested] = a #=> fails because "a" is a Ruby object, not a nested value
一种解决方案是将"A"存储为指针:
require 'ffi'
class A < FFI::Struct
layout :data, :int
end
class B < FFI::Struct
layout :nested, :pointer # we use a pointer, not a class
end
a = A.new
b = B.new
# Set some arbitrary data
a[:data] = 42
# Set :nested to the pointer to the "a" object
b[:nested] = a.pointer
# To prove it works, create a new object with the pointer
c = A.new(b[:nested])
# And prove we can get the arbitrary data
puts c[:data] #=> 42