34 lines
1.3 KiB
Rust
34 lines
1.3 KiB
Rust
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// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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// Various unsuccessful attempts to put the unboxed closure kind
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// inference into an awkward position that might require fixed point
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// iteration (basically where inferring the kind of a closure `c`
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// would require knowing the kind of `c`). I currently believe this is
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// impossible.
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fn a() {
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// This case of recursion wouldn't even require fixed-point
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// iteration, but it still doesn't work. The weird structure with
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// the `Option` is to avoid giving any useful hints about the `Fn`
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// kind via the expected type.
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let mut factorial: Option<Box<Fn(u32) -> u32>> = None;
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let f = |x: u32| -> u32 {
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let g = factorial.as_ref().unwrap();
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if x == 0 {1} else {x * g(x-1)}
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};
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factorial = Some(Box::new(f));
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//~^ ERROR cannot assign to `factorial` because it is borrowed
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}
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fn main() { }
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