45157fc58c
On reflection, the extra spaces around classes feels weird to me. Let's revert that (but keep the 2021 edition migration in place).
152 lines
3 KiB
Markdown
152 lines
3 KiB
Markdown
# Splices and toggles
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## Splices: `(foo)`
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Use `(foo)` syntax to insert the value of `foo` at runtime.
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Any HTML special characters are escaped by default.
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```rust
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let best_pony = "Pinkie Pie";
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let numbers = [1, 2, 3, 4];
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# let _ = maud::
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html! {
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p { "Hi, " (best_pony) "!" }
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p {
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"I have " (numbers.len()) " numbers, "
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"and the first one is " (numbers[0])
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}
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}
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# ;
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```
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Arbitrary Rust code can be included in a splice by using a [block].
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This can be helpful for complex expressions
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that would be difficult to read otherwise.
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```rust
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# struct Foo;
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# impl Foo { fn time(self) -> Bar { Bar } }
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# struct Bar;
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# impl Bar { fn format(self, _: &str) -> &str { "" } }
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# fn something_convertible_to_foo() -> Option<Foo> { Some(Foo) }
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# fn test() -> Option<()> {
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# let _ = maud::
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html! {
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p {
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({
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let f: Foo = something_convertible_to_foo()?;
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f.time().format("%H%Mh")
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})
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}
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}
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# ;
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# Some(())
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# }
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```
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[block]: https://doc.rust-lang.org/reference.html#block-expressions
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### Splices in attributes
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Splices work in attributes as well.
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```rust
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let secret_message = "Surprise!";
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# let _ = maud::
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html! {
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p title=(secret_message) {
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"Nothing to see here, move along."
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}
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}
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# ;
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```
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To concatenate multiple values within an attribute,
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wrap the whole thing in braces.
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This syntax is useful for building URLs.
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```rust
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const GITHUB: &'static str = "https://github.com";
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# let _ = maud::
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html! {
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a href={ (GITHUB) "/lambda-fairy/maud" } {
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"Fork me on GitHub"
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}
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}
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# ;
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```
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### Splices in classes and IDs
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Splices can also be used in classes and IDs.
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```rust
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let name = "rarity";
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let severity = "critical";
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# let _ = maud::
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html! {
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aside #(name) {
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p.{ "color-" (severity) } { "This is the worst! Possible! Thing!" }
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}
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}
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# ;
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```
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### What can be spliced?
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You can splice any value that implements [`std::fmt::Display`][Display].
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Most primitive types (such as `str` and `i32`) implement this trait,
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so they should work out of the box.
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To change this behavior for some type,
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you can implement the [`Render`][Render] trait by hand.
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The [`PreEscaped`][PreEscaped] wrapper type,
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which outputs its argument without escaping,
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works this way.
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See the [traits](render-trait.md) section for details.
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```rust
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use maud::PreEscaped;
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let post = "<p>Pre-escaped</p>";
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# let _ = maud::
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html! {
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h1 { "My super duper blog post" }
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(PreEscaped(post))
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}
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# ;
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```
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[Display]: http://doc.rust-lang.org/std/fmt/trait.Display.html
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[Render]: https://docs.rs/maud/*/maud/trait.Render.html
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[PreEscaped]: https://docs.rs/maud/*/maud/struct.PreEscaped.html
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## Toggles: `[foo]`
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Use `[foo]` syntax to show or hide something
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based on a boolean expression `foo`.
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This works on empty attributes:
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```rust
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let allow_editing = true;
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# let _ = maud::
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html! {
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p contenteditable[allow_editing] {
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"Edit me, I "
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em { "dare" }
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" you."
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}
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}
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# ;
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```
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And classes:
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```rust
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let cuteness = 95;
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# let _ = maud::
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html! {
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p.cute[cuteness > 50] { "Squee!" }
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}
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# ;
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```
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