46 lines
1.1 KiB
Rust
46 lines
1.1 KiB
Rust
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use std::cell::Cell;
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use std::fmt::{self, Display, Formatter};
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/// Implements fmt::Display by calling formatter on contents.
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pub(crate) struct Fmt<T, F> {
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contents: Cell<Option<T>>,
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formatter: F,
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}
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impl<T, F: Fn(T, &mut Formatter) -> fmt::Result> Fmt<T, F> {
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pub(crate) fn new(t: T, formatter: F) -> Self {
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Self {
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contents: Cell::new(Some(t)),
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formatter,
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}
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}
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}
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impl<T, F: Fn(T, &mut Formatter) -> fmt::Result> Display for Fmt<T, F> {
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/// fmt is single-use only.
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fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
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let contents = self.contents.replace(None).expect("only call Fmt::fmt once");
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(self.formatter)(contents, f)
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}
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}
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impl<I: IntoIterator<Item = T>, T: Display> Fmt<I, fn(I, &mut Formatter) -> fmt::Result> {
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/// Formats values with a comma and a space separating them.
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pub(crate) fn comma_separated(into_iter: I) -> Self {
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Self::new(into_iter, fmt_comma_separated)
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}
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}
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fn fmt_comma_separated<T: Display>(
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into_iter: impl IntoIterator<Item = T>,
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f: &mut Formatter,
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) -> fmt::Result {
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for (i, v) in into_iter.into_iter().enumerate() {
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if i > 0 {
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f.write_str(", ")?;
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}
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Display::fmt(&v, f)?;
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}
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Ok(())
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}
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