E0502 and encapsulated borrows

help
1

Hi,

I find the borrow checker has a strange behavior when borrows are encapsulated. For example the following code:

foo.fun0_with_imm_borrow(foo.fun1_with_mut_borrow());

is not accepted by the borrow checker, yet it is (should be?) equivalent to

let res = foo.fun1_with_mut_borrow();
foo.fun0_with_imm_borrow(res);

which does compile without problem.
Is there any reason behind this design?

Here is an example of the issue in the rust playground: Rust Playground

2

No, it's equivalent to below.

let callee = &foo;
let arg = foo.func1_with_mut_borrow();
Foo::func0_with_imm_borrow(callee, arg)

Method call syntax is a compiler assisted sugar for fully qualified function call, or UFCS(Univalsal Function Call Syntax). Check this chapter of the book for more details.

3

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