英文:
Is there any way to "early return" in a declarative macro iterations?
问题
我对Rust的宏很陌生。
我想找到一种实现类似这样行为的方法：在迭代中提前返回
我学到了我可以使用像这样的声明性宏生成元组：
fn function(input) -> Result<input_type, err_type> {
// 做一些事情
}
macro_rules! to_tuple {
($($input:expr),*) => (($( function($input), )*));
}
fn main() {
to_tuple!(i_1, i_2);
// 我会得到一个元组: (o_1, o_2)
}
现在我想在每次迭代中检查function的结果。如果它们都正常，我将得到一个Ok(tuple)。如果发生错误，我将得到一个Err(string)。就像这样：
to_tuple!(right_1, right_2) => Ok( (o_1, o_2) )
to_tuple!(right_1, right_2, right_3) => Ok( (o_1, o_2, o_3) )
to_tuple!(right_1, wrong_1, right_2) => Err( string )
使用声明性宏是否可能实现这个目标？
我认为宏生成的不是真正的迭代，所以没有迭代，因此显然没有"提前返回"。我希望我是错的。如果有人有任何想法，请告诉我。
英文:
I'm new to Rust's macros.
I'd like to find a way to achieve a behaviour like this: early return in iterations
I learned I can generate tuples using a declarative macro like this one:
fn function(input) -> Result<input_type,err_type> {
// do something
}
macro_rules! to_tuple {
($($input:expr),*) => (($( function($input), )*));
}
fn main() {
to_tuple!(i_1, i_2);
// I will get a tuple: (o_1, o_2)
}
Now I'd like to check result of function in every iteration. If they are all ok, I'll get a Ok(tuple). If error occurs, I'll get a Err(stirng). Like:
to_tuple!(right_1, right_2) => Ok( (o_1, o_2) )
to_tuple!(right_1, right_2, right_3) => Ok( (o_1, o_2, o_3) )
to_tuple!(right_1, wrong_1, right_2) => Err( string )
Is this possible using declarative macros?
I think what macros produces is not real iterations, so there is no iterations, therefore apparently there is no "early return". I wish I were wrong. If anyone has any idea, please tell me.
答案1
得分: 0
这将是一个完美的地方，适用于try块。 除了它们是不稳定的。 但我们可以用一个闭包来模拟它们：
macro_rules! to_tuple {
($($input:expr),*) => ((|| -> Result<_, String> { Ok(($( function($input)?, )*)) })());
}
英文:
This would be a perfect place for try blocks. Except they're unstable. But we can emulate them with a closure:
macro_rules! to_tuple {
($($input:expr),*) => ((|| -> Result<_, String> { Ok(($( function($input)?, )*)) })());
}
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