Setting of member of const struct should not be possible

[gwierzchowski]

In below listing the assignment line I think should not compile with error like "invalid left-hand side expression" - as it would be in case variable was not a struct.
PS: Moving const definition to the function body does not change anything.

pub struct Foo {
    bar: bool,
}
const CONF: Foo = Foo { bar: false };

fn main() {
    println!("main 0 {}", CONF.bar); // prints false - OK
    
    // This does compile ?!?
    CONF.bar = true;

    println!("main 1 {}", CONF.bar); // prints false - ?!?
}

(Playground)

Output:

main 0 false
main 1 false

Errors:

   Compiling playground v0.0.1 (/playground)
    Finished dev [unoptimized + debuginfo] target(s) in 0.39s
     Running `target/debug/playground`

[jonas-schievink]

This is working as expected – the LHS of an assignment must be a place expression, which a field access is. This should probably be warned against though, but that is covered by #16789, so closing in favor of that.

[gwierzchowski]

Got it.
As I understand assignment in my sample is equivalent to:

Foo { bar: false }.bar = true;

Thanks.