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https://gitee.com/openharmony/third_party_rust_quote
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Merge pull request #215 from dtolnay/comments
Touch up comments from PR #211
This commit is contained in:
David Tolnay
GitHub
commit
7c357e801a
136
src/lib.rs
136
src/lib.rs
@ -661,67 +661,74 @@ macro_rules! quote_bind_next_or_break {
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};
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}
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// The obvious way to implement this macro is as a tt muncher. This
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// implementation does something more complex, for two reasons.
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// - With a tt muncher it's easy to hit Rust's built-in `recursion_limit`,
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// which this implementation avoids because it isn't tail recursive.
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// - Compile times for a tt muncher are quadratic relative to the length of the
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// input. This implementation is linear, so it will be faster (potentially
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// much faster) for long inputs. However, the constant factors of this
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// implementation are higher than that of a tt muncher, so it is somewhat
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// slower than a tt muncher if there are many invocations with short inputs.
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// The obvious way to write this macro is as a tt muncher. This implementation
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// does something more complex for two reasons.
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//
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// - With a tt muncher it's easy to hit Rust's built-in recursion_limit, which
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// this implementation avoids because it isn't tail recursive.
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//
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// - Compile times for a tt muncher are quadratic relative to the length of
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// the input. This implementation is linear, so it will be faster
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// (potentially much faster) for big inputs. However, the constant factors
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// of this implementation are higher than that of a tt muncher, so it is
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// somewhat slower than a tt muncher if there are many invocations with
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// short inputs.
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//
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// An invocation like this:
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// ```
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// quote_each_token! { _s a b c d e f g h i j }
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// ```
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//
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// quote_each_token!(_s a b c d e f g h i j);
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//
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// expands to this:
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// ```
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// quote_tokens_with_context! (_s
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// (@ @ @ @ @ @ a b c d e f g h i j)
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// (@ @ @ @ @ a b c d e f g h i j @)
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// (@ @ @ @ a b c d e f g h i j @ @)
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// (@ @ @ (a) (b) (c) (d) (e) (f) (g) (h) (i) (j) @ @ @)
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// (@ @ a b c d e f g h i j @ @ @ @)
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// (@ a b c d e f g h i j @ @ @ @ @)
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// (a b c d e f g h i j @ @ @ @ @ @)
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// );
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// ```
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// which expands to this:
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// ```
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// quote_token_with_context! (_s @ @ @ @ @ @ a);
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// quote_token_with_context! (_s @ @ @ @ @ a b);
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// quote_token_with_context! (_s @ @ @ @ a b c);
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// quote_token_with_context! (_s @ @ @ (a) b c d);
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// quote_token_with_context! (_s @ @ a (b) c d e);
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// quote_token_with_context! (_s @ a b (c) d e f);
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// quote_token_with_context! (_s a b c (d) e f g);
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// quote_token_with_context! (_s b c d (e) f g h);
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// quote_token_with_context! (_s c d e (f) g h i);
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// quote_token_with_context! (_s d e f (g) h i j);
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// quote_token_with_context! (_s e f g (h) i j @);
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// quote_token_with_context! (_s f g h (i) j @ @);
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// quote_token_with_context! (_s g h i (j) @ @ @);
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// quote_token_with_context! (_s h i j @ @ @ @);
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// quote_token_with_context! (_s i j @ @ @ @ @);
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// quote_token_with_context! (_s j @ @ @ @ @ @);
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// ``
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// Without using recursion, we get one invocation of
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// `quote_token_with_context!` for each tt, with three tts of context on either
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// side. This is enough for the longest possible interpolation form (a
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// repetition interpolation with a separator, of the form `# (var) , *`) to be
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// fully represented with the first or last tt in the middle.
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//
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// quote_tokens_with_context!(_s
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// (@ @ @ @ @ @ a b c d e f g h i j)
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// (@ @ @ @ @ a b c d e f g h i j @)
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// (@ @ @ @ a b c d e f g h i j @ @)
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// (@ @ @ (a) (b) (c) (d) (e) (f) (g) (h) (i) (j) @ @ @)
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// (@ @ a b c d e f g h i j @ @ @ @)
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// (@ a b c d e f g h i j @ @ @ @ @)
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// (a b c d e f g h i j @ @ @ @ @ @)
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// );
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//
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// which gets transposed and expanded to this:
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//
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// quote_token_with_context!(_s @ @ @ @ @ @ a);
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// quote_token_with_context!(_s @ @ @ @ @ a b);
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// quote_token_with_context!(_s @ @ @ @ a b c);
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// quote_token_with_context!(_s @ @ @ (a) b c d);
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// quote_token_with_context!(_s @ @ a (b) c d e);
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// quote_token_with_context!(_s @ a b (c) d e f);
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// quote_token_with_context!(_s a b c (d) e f g);
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// quote_token_with_context!(_s b c d (e) f g h);
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// quote_token_with_context!(_s c d e (f) g h i);
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// quote_token_with_context!(_s d e f (g) h i j);
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// quote_token_with_context!(_s e f g (h) i j @);
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// quote_token_with_context!(_s f g h (i) j @ @);
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// quote_token_with_context!(_s g h i (j) @ @ @);
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// quote_token_with_context!(_s h i j @ @ @ @);
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// quote_token_with_context!(_s i j @ @ @ @ @);
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// quote_token_with_context!(_s j @ @ @ @ @ @);
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//
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// Without having used muncher-style recursion, we get one invocation of
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// quote_token_with_context for each original tt, with three tts of context on
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// either side. This is enough for the longest possible interpolation form (a
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// repetition with separator, as in `# (#var) , *`) to be fully represented with
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// the first or last tt in the middle.
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//
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// The middle tt (surrounded by parentheses) is the tt being processed.
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// - When it is a `#`, `quote_token_with_context!` can do an interpolation. The
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// interpolation kind will depend on the three subsequent tts.
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// - When it is within a later part of an interpolation, it can be ignored,
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// because the interpolation has already been done.
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// - When it is not part of an interpolation it can be treated normally.
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// - When it is a `@` it can be ignored.
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//
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// The parentheses around the middle tt aren't necessary, but they make the
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// macro definitions easier to read.
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// - When it is a `#`, quote_token_with_context can do an interpolation. The
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// interpolation kind will depend on the three subsequent tts.
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//
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// - When it is within a later part of an interpolation, it can be ignored
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// because the interpolation has already been done.
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//
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// - When it is not part of an interpolation it can be pushed as a single
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// token into the output.
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//
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// - When the middle token is an unparenthesized `@`, that call is one of the
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// first 3 or last 3 calls of quote_token_with_context and does not
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// correspond to one of the original input tokens, so turns into nothing.
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#[macro_export]
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#[doc(hidden)]
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macro_rules! quote_each_token {
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@ -738,7 +745,7 @@ macro_rules! quote_each_token {
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};
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}
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// See the comments on `quote_each_token`.
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// See the explanation on quote_each_token.
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#[macro_export]
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#[doc(hidden)]
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macro_rules! quote_each_token_spanned {
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@ -755,7 +762,7 @@ macro_rules! quote_each_token_spanned {
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};
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}
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// See the comments on `quote_each_token`.
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// See the explanation on quote_each_token.
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#[macro_export]
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#[doc(hidden)]
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macro_rules! quote_tokens_with_context {
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@ -770,7 +777,7 @@ macro_rules! quote_tokens_with_context {
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};
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}
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// See the comments on `quote_each_token`.
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// See the explanation on quote_each_token.
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#[macro_export]
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#[doc(hidden)]
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macro_rules! quote_tokens_with_context_spanned {
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@ -785,14 +792,15 @@ macro_rules! quote_tokens_with_context_spanned {
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};
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}
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// See the comments on `quote_each_token`.
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// See the explanation on quote_each_token.
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#[macro_export]
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#[doc(hidden)]
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macro_rules! quote_token_with_context {
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// `@` is the leading/trailing context character. Ignore it.
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// Unparenthesized `@` indicates this call does not correspond to one of the
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// original input tokens. Ignore it.
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($tokens:ident $b3:tt $b2:tt $b1:tt @ $a1:tt $a2:tt $a3:tt) => {};
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// A repetition interpolation with no separator.
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// A repetition with no separator.
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($tokens:ident $b3:tt $b2:tt $b1:tt (#) ( $($inner:tt)* ) * $a3:tt) => {{
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use $crate::__private::ext::*;
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let has_iter = $crate::__private::ThereIsNoIteratorInRepetition;
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@ -814,7 +822,7 @@ macro_rules! quote_token_with_context {
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// ... and one step later.
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($tokens:ident $b3:tt # ( $($inner:tt)* ) (*) $a1:tt $a2:tt $a3:tt) => {};
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// A repetition interpolation with a separator.
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// A repetition with separator.
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($tokens:ident $b3:tt $b2:tt $b1:tt (#) ( $($inner:tt)* ) $sep:tt *) => {{
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use $crate::__private::ext::*;
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let mut _i = 0usize;
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@ -856,8 +864,8 @@ macro_rules! quote_token_with_context {
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};
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}
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// See the comments on `quote_each_token`, and on the individual rules for
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// `quote_token_with_context`.
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// See the explanation on quote_each_token, and on the individual rules of
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// quote_token_with_context.
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#[macro_export]
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#[doc(hidden)]
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macro_rules! quote_token_with_context_spanned {
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