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Wrap enum_val_signed in an Option. #220

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Merged
merged 2 commits into from
Nov 6, 2016
Merged

Wrap enum_val_signed in an Option. #220

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15d1881
Wrap enum_val_signed in an Option.
Nov 6, 2016
fda0548
Restore outer conditional.
Nov 6, 2016
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14 changes: 9 additions & 5 deletions src/clang.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -349,11 +349,15 @@ impl Cursor {

/// Get the signed constant value for this cursor's enum variant referent.
///
/// Returns `LLONG_MIN` if the cursor's referent is not an enum variant,
/// which is also a valid enum value, so callers should check the cursor
/// kind before calling this method (see issue #127).
pub fn enum_val_signed(&self) -> i64 {
unsafe { clang_getEnumConstantDeclValue(self.x) as i64 }
/// Returns None if the cursor's referent is not an enum variant.
pub fn enum_val_signed(&self) -> Option<i64> {
unsafe {
if self.kind() == CXCursor_EnumConstantDecl {
Some(clang_getEnumConstantDeclValue(self.x) as i64)
} else {
None
}
}
}

/// Get the unsigned constant value for this cursor's enum variant referent.
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15 changes: 8 additions & 7 deletions src/ir/enum_ty.rs
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Expand Up @@ -72,18 +72,19 @@ impl Enum {

declaration.visit(|cursor| {
if cursor.kind() == CXCursor_EnumConstantDecl {
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why not keeping the if above as before, and then just unwrap the result of enum_val_signed?

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I like to avoid unwrapping when it's easy to do, because it makes the code here less intertwined with code elsewhere; if enum_val_signed changes to return None for some other reason, that's a future bug avoided. I also think once #128 lands, it'll look nice and clean.

I'm pretty new at rust though, and brand new to rust-bindgen, so if I'm missing some bigger picture reason why it's worth keeping the duplicate check, I'm happy to change it.

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I sort of agree, and in general it uses to be good advice. But in this case, IMO at least, this is inverting the dependency instead.

That is, if for some other reason enum_val_signed returns Some when it's not a CXCursor_EnumConstantDecl, the code meaning is completely different, and we're in trouble.

We're traversing the ast looking for EnumConstantDecl nodes, so I think that if should stay there instead of relying that this only returns Some if that's the case.

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Makes sense. Here's a new version with the outer if, but still without unwrap(), for the reason above. If I understand rust correctly, there shouldn't be any runtime time penalty, right?

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I don't think there's a runtime penalty for using unwrap vs if let. Maybe rust annotates unwrap as unlikely so it has a bit better branch prediction, but nothing measurable for this case I think :)

let name = cursor.spelling();
let comment = cursor.raw_comment();
let val = if is_signed {
EnumVariantValue::Signed(cursor.enum_val_signed())
let value = if is_signed {
cursor.enum_val_signed().map(EnumVariantValue::Signed)
} else {
EnumVariantValue::Unsigned(cursor.enum_val_unsigned())
Some(EnumVariantValue::Unsigned(cursor.enum_val_unsigned()))
};
variants.push(EnumVariant::new(name, comment, val));
if let Some(val) = value {
let name = cursor.spelling();
let comment = cursor.raw_comment();
variants.push(EnumVariant::new(name, comment, val));
}
}
CXChildVisit_Continue
});

Ok(Enum::new(repr, variants))
}
}
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