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Weird macro + type check behavior #22355
Description
Sorry for the bad title of this issue
use serialize::json;
use std::iter::Map;
extern crate serialize;
macro_rules! expect_f64 {
($value:expr) => (try!(
match $value.as_f64() {
Some(v) => Ok(v),
None => Err("Expected f64 value")
}
))
}
fn main() {
let v = vec![json::Json::F64(1.0)];
let m: Map<f64, _> = v.iter().map(|p| expect_f64!(p));
} Compiling jsonn v0.0.1 (file:///private/tmp/jsonn)
src/lib.rs:19:43: 19:58 error: mismatched types:
expected `core::result::Result<_, _>`,
found `f64`
(expected enum `core::result::Result`,
found f64) [E0308]
src/lib.rs:19 let m: Map<f64, _> = v.iter().map(|p| expect_f64!(p));
^~~~~~~~~~~~~~~
src/lib.rs:19:26: 19:58 error: mismatched types:
expected `core::iter::Map<f64, _>`,
found `core::iter::Map<core::slice::Iter<'_, serialize::json::Json>, [closure src/lib.rs:19:39: 19:58]>`
(expected f64,
found struct `core::slice::Iter`) [E0308]
src/lib.rs:19 let m: Map<f64, _> = v.iter().map(|p| expect_f64!(p));
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
error: aborting due to 2 previous errors
Could not compile `jsonn`.
To learn more, run the command again with --verbose.
For some reason, the compiler expects that closure to return a Result instead of an f64. It might have to do with using macros in a closure?
Activity
frewsxcv commentedon Feb 15, 2015
Nevermind, tjakubow on IRC helped me debug this
Merge pull request rust-lang#22355 from WaterWhisperer/diagnostic-non…