Let Chains in Rust 1.88: Cleaner Conditionals and the 2024 Edition Requirement

Let chains solve the nested if-let pyramid

If you’ve been writing Rust for any length of time, you know this pattern:

if let Some(user) = get_user(id) {
    if let Some(email) = user.email {
        if email.is_verified() {
            send_welcome(&email);
        }
    }
}

Three levels of nesting for three conditions. It works, but each layer pushes the actual logic further right and makes the intent harder to read at a glance. Rust 1.88 shipped let chains as a stable feature, and they address this directly.

if let Some(user) = get_user(id)
    && let Some(email) = user.email
    && email.is_verified()
{
    send_welcome(&email);
}

One block, one body. The conditions still short-circuit left to right, so email.is_verified() only runs if the two let bindings succeed first.

How let chains actually work

You chain pattern matches and plain boolean conditions together with && inside an if or while. They can appear in any order — you don’t have to lead with let:

if count > 0
    && let Some(first) = items.first()
    && first.is_active()
{
    process(first);
}

Each binding is in scope for the rest of the chain and for the body of the block. That scoping rule is also why a let can’t appear inside parentheses or on the right side of || — the RFC that landed this feature kept the scoping model intentionally simple. One chain, left to right, no branching.

The while form works identically:

while let Some(task) = queue.pop()
    && task.priority > THRESHOLD
{
    execute(task);
}

This replaces the old pattern of a while let with an inner if guard — a small thing, but it flattens the loop body.

The edition requirement that trips everyone up

Let chains only work under the Rust 2024 edition. Try to compile them on an older edition and the compiler gives you a parse error with no suggestion about what to change. The fix is one line in Cargo.toml:

[package]
name = "my-crate"
edition = "2024"

Projects created recently with cargo new already default to 2024. Older codebases sitting on 2021 — or even 2018 — are the ones that silently miss this. Check the [package] section before assuming let chains don’t work.

Migrating an existing codebase is usually straightforward. Running cargo fix --edition after bumping the edition handles most mechanical changes automatically. For a workspace, each member’s Cargo.toml needs to be updated individually. The Rust edition guide walks through everything that actually changed between 2021 and 2024, and it’s a shorter list than you might expect.

The other two features in Rust 1.88

Let chains got the most community attention, but two other features shipped in the same release.

Naked functions

The #[naked] attribute is now stable. A naked function has no compiler-generated prologue or epilogue — the body is exactly what you put in an asm! block and nothing else. This is deliberately niche. If you write interrupt handlers, bootloader code, or context-switching logic in Rust, the attribute gives you complete control over the generated assembly without workarounds or separate .s files.

Cargo cache cleanup

Cargo now runs automatic garbage collection on its home-directory cache. Files downloaded from the network get removed if they haven’t been accessed in three months. On a machine where you try out many crates over time, the cache can silently grow into several gigabytes. This keeps it self-managing with no manual intervention or plugin required.

Sources

• blog.rust-lang.org
• doc.rust-lang.org
• rust-lang.github.io
• phoronix.com
• blog.jetbrains.com
• smallcultfollowing.com
• blog.rust-lang.org
• doc.rust-lang.org