Temporary value dropped while borrowed using Closure

To solve this error
"the size for values of type (dyn std::ops::Fn() + 'static) cannot be known at compilation time"

I added on_click: Option<&'static dyn Fn() -> ()>

But now I am unsure how to solve
"temporary value dropped while borrowed"

fn main(){
let initial_state = 5;
fn handler(val: i32) {
       val + 1;
let props = Props { on_click: Some(&|| handler(initial_state))};

struct Props {
   on_click: Option<&'static dyn Fn() -> ()>

How do I make initial_state live long enough?

By using &'static you are telling the compiler that the closure must be an immutable compile time constant, so you can't store a local variable such as initial_state inside it. Use a Box instead.

struct Props {
   on_click: Option<Box<dyn Fn() -> ()>>
1 Like

You will probably also need to annotaye your closure with move

move || handler(initial_state)

If you want to see how closures are desugared, you can read my blog on the subject:

1 Like

@RustyYato Thank you, I will read your blog on closures. I am working with the wasm crate right now and am running into many issues regarding closures and lifetime's.

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