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Add messages to Option's and Result's must_use annotation for is_* #62431

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Jul 13, 2019
Merged

Add messages to Option's and Result's must_use annotation for is_* #62431

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145385e
Add messages to Option and Result must_use for is_*
czipperz Jul 6, 2019
9b0623d
Wrap line
czipperz Jul 6, 2019
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5 changes: 3 additions & 2 deletions src/libcore/option.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -178,7 +178,7 @@ impl<T> Option<T> {
/// ```
///
/// [`Some`]: #variant.Some
#[must_use]
#[must_use = "if you intended to assert that this has a value, consider `.unwrap()` instead"]
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
pub fn is_some(&self) -> bool {
Expand All @@ -201,7 +201,8 @@ impl<T> Option<T> {
/// ```
///
/// [`None`]: #variant.None
#[must_use]
#[must_use = "if you intended to assert that this doesn't have a value, consider \
`.and_then(|| panic!(\"`Option` had a value when expected `None`\"))` instead"]
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I think this message is too long. How about the suggestion is .ok_or(()).unwrap_err()?

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I don't have a strong opinion; I just wanted to give a message as nice as the .unwrap() ones do.

Maybe there's a way to combine them? .ok_or("Option::None").unwrap_err() or similar?

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Can we just tell the user to wrap it in an assert!()?

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Really we should add an expect_none.

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See #62596.

#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
pub fn is_none(&self) -> bool {
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4 changes: 2 additions & 2 deletions src/libcore/result.rs
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Expand Up @@ -277,7 +277,7 @@ impl<T, E> Result<T, E> {
/// let x: Result<i32, &str> = Err("Some error message");
/// assert_eq!(x.is_ok(), false);
/// ```
#[must_use]
#[must_use = "if you intended to assert that this is ok, consider `.unwrap()` instead"]
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
pub fn is_ok(&self) -> bool {
Expand All @@ -302,7 +302,7 @@ impl<T, E> Result<T, E> {
/// let x: Result<i32, &str> = Err("Some error message");
/// assert_eq!(x.is_err(), true);
/// ```
#[must_use]
#[must_use = "if you intended to assert that this is err, consider `.unwrap_err()` instead"]
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
pub fn is_err(&self) -> bool {
Expand Down