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Improve the comment for cs_fold1

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varkor 2018-04-12 01:33:52 +01:00
parent 88a9c69121
commit 60dc4f8ec8
1 changed files with 9 additions and 2 deletions
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11
src/libsyntax_ext/deriving/generic/mod.rs
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@ -1745,8 +1745,15 @@ pub fn cs_fold<F>(use_foldl: bool,
}
}
/// Special version of `cs_fold` that uses the result of a function call on the first field
/// as the base case when is at least 1 field, and the usual base case when there are zero fields.
/// Function to fold over fields, with three cases, to generate more efficient and concise code.
/// When the `substructure` has grouped fields, there are two cases:
/// Zero fields: call the base case function with None (like the usual base case of `cs_fold`).
/// One or more fields: call the base case function on the first value (which depends on
/// `use_fold`), and use that as the base case. Then perform `cs_fold` on the remainder of the
/// fields.
/// When the `substructure` is a `EnumNonMatchingCollapsed`, the result of `enum_nonmatch_f`
/// is returned. Statics may not be folded over.
/// See `cs_op` in `partial_ord.rs` for a model example.
pub fn cs_fold1<F, B>(use_foldl: bool,
f: F,
mut b: B,