0001 — class and active_class are &'static str

• Status: accepted
• Date: 2026-05-12
• Deciders: RAprogramm

Context

NavLinkProps exposes two CSS-class slots:

#![allow(unused)]
fn main() {
#[prop_or("nav-link")]
pub class: &'static str,

#[prop_or("active")]
pub active_class: &'static str,
}

The natural alternatives in the Yew ecosystem are AttrValue (an internally Rc<str>-backed handle used by attribute values) and Classes (an internal Vec<AttrValue> with deduplication and lazy join). Both accept runtime-built strings; &'static str does not.

The question is whether the cost of &'static str — consumers cannot pass an interpolated class list — outweighs the cost of the alternatives: an allocation on every render, a deeper trait stack, and a less obvious “what is this argument” answer for newcomers.

Decision

Keep &'static str for both class slots.

The crate’s contract is that class slots configure the wrapper. A consumer who needs runtime classes composes them on the parent element or via a tailwind/CSS-in-JS layer, not by funnelling a format!("{}{}", …) through NavLink. The 99% case is a literal class name; making literals zero-cost is the right trade.

For the breadcrumb chain and other components where class composition is unavoidable, those props use Classes directly. The asymmetry is deliberate: NavLink is the hot path, breadcrumbs are not.

Consequences

Positive

• Zero allocation per render for the common case.
• Compile-time enforcement that class names are constants — a String built from user input cannot land in a CSS class slot, eliminating a class of HTML-injection footguns at the type level.
• NavLinkProps: Copy-ish: every field is trivially clonable, making #[derive(Clone, PartialEq)] cheap.

Negative

• A consumer who needs runtime class composition on NavLink specifically cannot do it through the prop. They must either lift the class to the parent or wrap NavLink in their own component.
• The breadcrumb-vs-NavLink asymmetry is a small surprise for new readers and is documented in docs/ARCHITECTURE.md.

Cost to reverse

Moderate. Switching to AttrValue is a semver-breaking signature change across the public props of NavLink. The internal build_class helper would also need to grow an allocation path. No data migration; consumer upgrade is one-line per call site.