How to apply a function to certain fields of a struct

help
1

Hi,

Here is the playground

Basically, I want to specify the fields. I want to do something using a vector of some kind.

  1. Not sure how to specify the fields in the vector
  2. I am not sure how to use the fields in the vector. to get to the struct fields.

In Javascript, I would be able to place the fields as strings in an array ["person_a"]. then iterate the array, then call say_hello(bus[field]);

fn main() {
  let bus = Bus{
      person_a:70,
      person_b:56,
      person_c:35,
  };
  
  // 1. let v = ["person_a","person_c"];
  
  // 2. then apply a function to only those fields
  
}


struct Bus{
   person_a:i64,
   person_b:i64,
   person_c:i64
}

fn say_hello(field:i64){
   println!("hello {}",field);
}
2

This looks like mistake 6c from the well known list. Or maybe XY problem.

Indeed. This works because Javascript doesn't have struct types. What is does have is language-provided hash map. And, of course, if you would use HashMap instead of struct in Rust what you want would be trivial.

I don't recommend you to do this, though: because Javascript doesn't have struct types on language level Javascript JIT-compilers do a lot of work to recognize a situation where hash map is used like a struct and try to convert hash map into struct when that makes some sense. With transparent fallback back to full-blown hash map if you pick the other code path.

Rust assumes that if you need a struct you would, indeed, use struct. What's the “business task” you are trying to solve here?

3

Actually I suspect HashMap<&'static str, i32> is exactly what OP want, given field name student_{a, b, c}. OP is more likely confused what Rust struct means and used wrong tool.

4

OK, thank you. I will look into using hashmaps instead of structs.

5

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