offsetof¶
An offsetof
expression returns the byte offset of an instance variable in a struct or class type. It accepts the type as first argument and the instance variable name prefixed by an @
as second argument:
offsetof(Type, @ivar)
This is a low-level primitive and only useful if a C API needs to directly interface with the data layout of a Crystal type.
Example:
struct Foo
@x = 0_i64
@y = 34_i32
end
offsetof(Foo, @y) # => 8