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This post is auto-generated from RSS feed The Rust Programming Language Forum - Latest topics. Source: Passing a function as parameter: as reference or as value?

What is the difference if I define a function parameter as reference or as value (other that the parameter is moved)? Is there a performance difference?

pub fn calculate(
    data: &[SomeStruct],
    config: &Config,
    f_result_analyzer: &dyn Fn(&ResultBatch) -> i32,
) {...}

In this case I cannot remove the & before dyn and must pass the function as reference, as otherwise the compiler complains the size cannot be known at compile time. This makes sense, as anyhow only the address of the function is passed (or not?).

But I can rewrite the definition to

pub fn calculate<F>(
  data: &[SomeStruct],
  config: &Config, 
  f_result_analyzer: &F) 
where
    F: Fn(&ResultBatch) -> i32,
{...}

and also as value (note missing & before F):

pub fn calculate<F>(
  data: &[SomeStruct],
  config: &Config, 
  f_result_analyzer: F) 
where
    F: Fn(&ResultBatch) -> i32,
{...}

So I wonder: Is there any difference between the last two definitions?

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