在过去，此代码已编译，但最近不再被接受（我相信自RFC 738以来）。我想对参数进行参数化VertexBuffer，但实际上并没有任何顶点，而是GPU拥有了顶点，而该结构仅拥有了OpenGL buffer_id：
pub struct VertexBuffer<V: Vertex> {
buffer_id: GLuint,
num_vertices: usize,
}
该new函数填充缓冲区：
impl<V: Vertex> VertexBuffer<V> {
pub fn new(data: &Vec<V>) -> VertexBuffer<V>
{
let buffer_id = unsafe {
let mut id: GLuint = 0;
gl::GenBuffers(1, &mut id);
gl::BindBuffer(gl::ARRAY_BUFFER, id);
gl::BufferData(gl::ARRAY_BUFFER,
(mem::size_of::<V>() * data.len()) as GLsizeiptr,
mem::transmute(&data[0]),
gl::STATIC_DRAW);
id
};
VertexBuffer {
buffer_id: buffer_id,
num_vertices: data.len(),
}
}
....
}
我现在得到这些错误：
src/vertex_buffer.rs:10:25: 10:26 error: parameter `V` is never used
src/vertex_buffer.rs:10 pub struct VertexBuffer<V: Vertex> {
src/vertex_buffer.rs:10:25: 10:26 help: consider removing `V` or using a marker such as `core::marker::PhantomData`
src/vertex_buffer.rs:10 pub struct VertexBuffer<V: Vertex> {
仅供参考，隐含的其他函数，例如pre_render（）和post_render（）使用V类型来完成其工作，调用诸如
let attribute_data = Vertex::attribute_data(None::<V>);
您没有显示足够的代码来排除这种情况，因此建议您将类型移至函数：
impl VertexBuffer {
pub fn new<V: Vertex>(data: &Vec<V>) -> VertexBuffer<V> {
let buffer_id = unsafe {
let mut id: GLuint = 0;
gl::GenBuffers(1, &mut id);
gl::BindBuffer(gl::ARRAY_BUFFER, id);
gl::BufferData(gl::ARRAY_BUFFER,
(mem::size_of::<V>() * data.len()) as GLsizeiptr,
mem::transmute(&data[0]),
gl::STATIC_DRAW);
id
};
VertexBuffer {
buffer_id: buffer_id,
num_vertices: data.len(),
}
}
....
}
如果确实需要使用PhantomData，请尝试以下操作：
struct VertexBuffer<V> {
buffer_id: u32, // or whatever
num_vertices: u32, // or whatever
marker: std::marker::PhantomData<V>,
}
impl<V: Vertex> VertexBuffer<V> {
pub fn new(data: &Vec<V>) -> VertexBuffer<V> {
let buffer_id = unsafe {
let mut id: GLuint = 0;
gl::GenBuffers(1, &mut id);
gl::BindBuffer(gl::ARRAY_BUFFER, id);
gl::BufferData(gl::ARRAY_BUFFER,
(mem::size_of::<V>() * data.len()) as GLsizeiptr,
mem::transmute(&data[0]),
gl::STATIC_DRAW);
id
};
VertexBuffer {
buffer_id: buffer_id,
num_vertices: data.len(),
marker: std::marker::PhantomData,
}
}
....
}
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